PC turns on sometimes, others no chance.

I had a client give let me look at their old computer which would not switch back on following a hard unexpected shutdown. Where clients monitor was still on saying 'No signal detected'. The client then tried to turn the computer back on with no success, nothing at all, no sound of the computer attempting to boot, seemingly no power.

The computer is around 4-5 years old so first thought was the motherboard or power supply. Upon receiving the computer I attempted to start it up, and it did, got into Windows Vista (yuck!) and then I was able to use as normal.

So quickly I copied all the content from the PC to a USB drive just in case this was a fluke. Turns out it was a fluke, as I tried to shutdown and then turn the PC on again I witnessed what the client described, no power, no lights.

Since at this stage I was thinking definitely power supply and motherboard and that it could cost a bit to replace if its a motherboard that has become faulty, the client decided not to proceed with diagnostics and that they would buy a new PC, the most important part was the data is recovered. Fair enough, so I gave the  PC back and everyone was happy.

Seeing as though the client had the computer originally built by a friend who knows hardware, the client took the computer back to their friend to get a second opinion. Long story short the friend apparently found what the issue was, the CMOS battery had died or become faulty. Usually when this happens I find the BIOS tells you that the battery is low or CMOS memory mismatch etc, this computer no signs.

Standard CMOS Battery

Replacement of the battery is cheap, so just another thing I can check in the future when diagnosing faulty hardware next time.