A few months ago, my monitor started playing up - going blank. Powering down for a while seemed to get it going again. Usually on restart, the BIOS or CMOS would say the settings were wrong. I thought it was overheating, but when the monitor finally stopped working altogether, my PC shop diagnosed a kaput motherboard and I bought a new one.

Now it's happening all over again.

Does anyone have any ideas as to what could be causing it? Could it be a "dirty" power supply? If so, how can I tell?

Appreciate any advice.

Take the power supply to your local shop and have them test it...Also, bad power supplies sometimes smell like cat urine. I guess I have never heard the term 'dirty' power supply (which means nothing). Either they work, or they don't. They are not that expensive to replace. My local comp. shop sold me a 500W for $38.

Can you reveal what type and make of motherboard ? I have heard the term "dirty " in reference to electrical power. It refers to a power source that has a lot of spikes and swings in amplitude. Hence that is why some , installations require a power regulator (cleaner ? ) to maintain the power requirements. Most computers use 5 & 12 VDC.

In power supplies like anything else you normally get what you pay for. A bargain basement 18 dollar one is not going to perform like a 75 dollar one. Power supplies are not mentioned when everyone list their stats on their machines. Yet it is tantamount to trying to run a race car on economy grade gasoline..I will not build one with a cheap power supply as you are only asking for problems.

Also how recent did your shop replace your motherboard. Their work ought to carry some guarantee with it. If they misdiagnosed the problem this should be their worry and not yours.