Practical guide · verified against the real thing
Blue screen? Read the stop code first - the triage order that narrows it
In one line: A BSOD is Windows shutting down to protect itself and leaving a name behind. The stop code, the 'what failed' module, and what changed recently do most of the diagnosis before any tool runs.
The symptom: the screen goes blue, Windows says it ran into a problem and restarted, and you are left with a stop code - sometimes with a module name after "What failed:". A blue screen is not a verdict on the machine; it is Windows halting itself to avoid writing corruption, and naming the neighbourhood the fault came from.
Likely causes, most common first
A driver or a piece of software misbehaving (by far the most common); a recent change - new hardware, new driver, new update, new app - that the crash timeline lines up with; failing memory; a drive that is failing or full enough that swap and system files misbehave; heat pushing marginal hardware over. Notice the order: software and recency before hardware, because they are cheaper to prove.
Diagnosis
First, write the stop code and the failed module down or photograph them - they are the entire lead. Then ask what changed in the days before the first crash. Microsoft's own basic sequence is the right one: remove any newly added hardware and restart; if the machine will not stay up, start in safe mode and work from there; open Device Manager and look for the exclamation mark, updating or rolling back that driver; check free disk space, because Windows and many apps need room for swap. If the crashes continue, go one level deeper: the Windows Memory Diagnostic (mdsched.exe) for an overnight RAM pass, Event Viewer's system log for critical errors in the same timestamp window as the crash, and your update history for a driver or patch that landed just before the first blue screen.
Fix
Match the fix to the evidence: rollback or clean-reinstall the named driver; uninstall the update or app whose arrival matches the first crash; replace the stick the memory diagnostic flags; free space or replace a drive that is full or failing. A single blue screen after a power cut or a bad update needs no campaign - one clean reboot and watchfulness is a legitimate response.
When this fix will not work
The same stop code recurring after driver, memory, disk and recency checks have all come back clean is the pattern that moves the suspicion to hardware under load or to heat - and to the thermal triage if the machine is a laptop that runs hot. Random stop codes (a different one every time) point at memory or power delivery more than at any driver.
When to escalate
Before a repair shop or a warranty claim, assemble the evidence pack: the stop codes photographed, the memory-diagnostic result, and the Event Viewer window around one crash. That package is what turns "my computer bluescreens" into a covered fault. And back up first, always - a machine that crashes unpredictably is a machine that can die mid-session, and the backup is the part of this you actually care about in five years. If the machine is old and the fault is board-level, run the arithmetic on repair vs replace before authorising board work.
Official documentation (checked 16 September 2026): Microsoft, Troubleshooting Windows unexpected restarts and stop code errors (remove new hardware, safe mode, Device Manager, free space, Event Viewer in the advanced set).
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