I've got an old machine that crashes and restarts during the Windows boot process, but not always. It always does eventually make it through and get to the login screen, but it will take anywhere from no crashes to a half hour or so (I tend to just leave it and walk away) of crash-and-repeat cycles before it does.
So far I have left memtest86 run overnight which found no errors. Multiple chkdsk runs (done from a successful boot and scheduling it for next restart) usually don't any errors, though occasionally the crash will mess up an index that gets repaired during the boot up chkdsk.
When it crashes during a safe mode boot it actually shows an IRQL_NOT_LESS_OR_EQUAL error which I looked into and traced to occur during the loading of hal.sys, which I restored from the recovery console though I didn't expect it to help, and it didn't.
It only ever crashes during the boot up, never during use once it is up and running. If it was a hardware/drive fault, or the PSU going bad, I would expect it to also crash at other times or when under high load, but nope.
I could reinstall Windows, but if it actually is a hardware issue that'd be a waste of time. I'm out of ideas and google isn't being very helpful. Anyone know what's up?