I came across a strange problem today.

PC would boot into safe mode, but booting to normal mode would cause it to freeze at the windows logo screen (the one with the scrolling bar at the bottom).

The customer says that at some point, it wouldn’t shut down.

I open it up, in case one of the CDROM drives has developed a fault, and its drivers are causing the windows lockup… I remove power from both CDROM drives, but almost no difference.

After a few restarts, I can see some really strange behaviour… after XP is shutdown, the PSU fan keeps spinning… in fact, the PSU fan never stops until the power cord is removed (and restarts when it’s plugged in again)… PC sometimes won’t start via the power button, and sometimes the reset button makes it start.

I also discuss with the customer, the option of getting a new PC. She was considering it towards the end of this year, but recognises that she might have to upgrade earlier.

I figure this problem could be anything, so I take it back to the office, image the drive (in case the HDD is about to fail). I’m starting to think a MoBo or CPU failure… Maybe the PSU, but unlikely, given the symptoms.

Then I decide to try a different power supply (simply because a replacement MoBo or CPU (AMD Duron 750Mhz) would be more difficult to find). To my surprise, everything works flawlessly.

This is the first time I’ve seem a PSU fail like this. Normally they just go bang, or lose a voltage (so that some components keep going while others fail to start), or suddenly cut out at some point after powerup.

Its almost as if a voltage was just out of tolerance (too high or too low), such that the CPU (or some other critical component), would stop working when it was asked to do too much…

Anyway, I replace the PSU, and return the PC to a very relieved lady.