When a computer refuses to boot, shows a blue screen, or just goes black, most people assume the worst. In practice, the large majority of these problems do not need a repair shop or a full reinstall. Work through them on a ladder from soft to hard and from light to heavy: start with the cheapest steps that rule out temporary faults, then move into system repair, and leave hardware checks and reinstalling for last. Before you start, figure out which layer the fault sits in. A machine that will not turn on, one that boots but blue screens, and one that only misbehaves after you reach the desktop each need a different entry point and a different set of tools. Windows ships with repair tools that handle more than 80% of software-layer faults, and they never require third-party software, which keeps your data out of harm's way.
Step 1: The lightest checks (under a minute)
This step stays outside the system internals and rules out external causes in under a minute:
- Restart. A restart clears a large share of temporary faults such as memory leaks and stuck services. Many glitches are just the running state going wrong; once the system reinitializes, the fault often disappears on its own.
- Check power and connections. On a laptop, look at the charging light. On a desktop, make sure the motherboard's 24-pin and the CPU 4+4-pin power connectors are seated. Loose power contacts alone can stop a machine from booting or cut power mid-session.
- Swap the monitor or cable. A black screen can just as easily be a loose cable or a failed display. Swapping in a known-good set is faster than opening the case.
- Clear CMOS. If the machine restarts repeatedly or the clock keeps resetting, pull the power, remove the coin-cell battery for a few dozen seconds, and let the motherboard discharge to reset the BIOS. Wrong BIOS settings can cause endless restarts or a zeroed clock, and discharging restores the defaults.
Step 2: Boot into Safe Mode for precise troubleshooting
Safe Mode loads only the bare minimum drivers and startup items. If the system runs fine in this mode, the problem most likely lives in a recent driver or a self-starting program, and your search narrows at once.
To get in: hold Shift while clicking Restart at the login or desktop, then choose Troubleshoot > Advanced options > Startup Settings, restart, and press F4 to enter Safe Mode.
Work through the items below in Safe Mode. If you still blue screen here, the cause is probably not a driver or startup program, so do not keep digging at this layer and move on:
- Device Manager. Find any device with a yellow exclamation mark, right-click it, and choose Update driver or Roll back driver. Focus on the graphics card, sound card, and network adapter. Rolling back returns the driver to its previous working version; since recent blue screens are usually caused by a new driver, rollback tends to be the most effective fix.
- Windows Memory Diagnostic. Search the Start menu for "Windows Memory Diagnostic," then reboot and let it check the RAM automatically.
- Disable startup items. In Task Manager, go to the Startup tab, disable everything, reboot into normal mode, then re-enable items one at a time to find the culprit.
Step 3: Repair system files from the command line
Open a command prompt as administrator and run these in order:
sfc /scannow
DISM /Online /Cleanup-Image /RestoreHealth
chkdsk C: /f /r
sfc /scannowscans for and repairs corrupted system files, taking roughly 10 to 15 minutes.DISM /Online /Cleanup-Image /RestoreHealthrepairs the Windows image source and needs an internet connection to download the fixes.chkdsk C: /f /rchecks and repairs disk errors. The/fswitch fixes file-system errors and/rlocates bad sectors; on the system drive this runs after a reboot.
The three commands do different jobs, so run them all in order: SFC replaces corrupted files, DISM fixes where those files come from, and chkdsk handles the disk itself. They are the first repair step for system-layer faults.
Step 4: Startup Repair and System Restore
- Startup Repair. Go to Settings > Update & Security > Recovery > Restart now, then Troubleshoot > Advanced options > Startup Repair. It targets a broken boot configuration, runs fully automatically, asks for no parameters, and you just read the result when it finishes.
- System Restore. In the same Advanced options screen, choose System Restore to roll back to a restore point from the last seven days. It keeps your personal files and does not reinstall software; think of it as rewinding the system to a known-good state. The catch is that System Protection must have been turned on beforehand.
A good habit is to open Control Panel > System > System Protection and enable protection for drive C, then create restore points on a schedule. That insurance pays off exactly when you need it.
Reading blue screen (BSOD) stop codes
Note the stop code at the bottom of the blue screen and search it before you try anything. That alone saves a lot of blind guessing. The common pairings:
| Stop code | Likely cause |
|---|---|
| DRIVER_IRQL_NOT_LESS_OR_EQUAL | Driver conflict (network, sound, or graphics) |
| PAGE_FAULT_IN_NONPAGED_AREA | Memory or driver |
| CRITICAL_PROCESS_DIED | Corrupted system files (use SFC/DISM) |
| MEMORY_MANAGEMENT | Memory failure |
| VIDEO_TDR_FAILURE | Graphics driver or graphics hardware |
The same code can mean different things on different machines. Its job is to shrink the search area; you still have to combine it with what you were doing right before the crash.
Still won't boot: know when to stop
If you have climbed the whole ladder and the machine still will not start, stop forcing restarts and trying again. In these cases, take it to a professional, because DIY attempts can make things worse:
- 🔴 Blue screens with different codes each time. This points to memory or motherboard hardware failure and needs a diagnostic card.
- 🔴 Stuck at the BIOS, cannot enter the system. The boot loader is broken or the system drive has failed.
- 🔴 Suspected ransomware or rootkit. Standard tools will not find it; it needs professional removal.
- 🔴 The drive makes noise or smells burnt. Physical damage. Cut the power immediately.
- 🔴 Data loss. Working on a failed drive yourself destroys the chance of recovery. Hand it to a data recovery service.
Key reminders
- Before changing drivers or reinstalling, always create a restore point and back up your data first.
- Do not manually delete "system files" you do not recognize, and do not run registry cleaners that delete things blindly.
- Only consider a clean install of Windows (see the reinstall tutorial) after software fixes fail and the hardware checks out. It is often the final answer, but it wipes drive C. By default your desktop, Documents, and Downloads all live on C, so move important files to another partition or an external drive before you start.