PCIe video card question

My wife has a Presario/HP PC which we added an Nvidia 8600 GT card into a few years back. It has worked fine until a week or so ago. My wife told me when I got home that her PC wasn't working, so I tried to boot it up. There was no signal getting to the monitor. This PC is about 7 years old. This is what I checked. I used a different monitor. Same problem. I plugged the monitor cable into the onboard connection. Still nothing. I wised up and removed the 8600 from the PCIe, then plugged the cable into the onboard slot. We got video display then. Because of the age of the PC, I checked for leakage or bulging capacitors. Nothing visible. I plugged the 8600 into my PC and it worked fine. We bought another video card to try. It didn't work, but the minimum specs for the card were below what her PC has. Here PC has a Sempron processor and it required a higher Athlon.

Here is what the PC does/did. When it first starts up, the fan(s) seem to "roar" for a couple of seconds, but settles down to normal. This is what this PC has done since coming out of the box and I consider it normal. Over the past few months, it has been a bit noisier from time to time. When it was louder, I pulled it out to see where the noise was coming from. I determined it was coming from the power supply, but it did not do it all the time. The PS is CoolerMaster 500w. With the 8600 out, there has been no more noise from it since. When the "no signal" problem was happening (with the 8600 and the new card) the "roar" was constant until I did a hard shut down.

I haven't heard of a PCIe slot going bad per se. I tried to look to see is port was somehow disabled, but without the card installed, it didn't show up.

Does anyone have any ideas? I have a bit more than basic knowledge of PCs, but nothing compared to those of you on here. We plan to replace the tower in a couple of months, but my wife is Jonesing for her Sims games.

 

Your description of the problem is indicitive of a power supply that is no longer providing sufficient voltage for the application. Over a period of time the output from a power supply diminishes. You most likely need a new power supply for the machine.