'Old' system means its well out of warranty so pull the ps from the case. Remove the four screws and remove the cover. Don't touch anything but blow it out with canned air. If you really want to be thorough, keep it unplugged for a couple of days so the capacitors can drain and you can get in there with a small (1") paint brush (I prefer natural bristle rather than plastic bristle) and brush all the nooks and crannies to loosen the dust. Get it as clean as you can. Reassemble and test. If its an AT ps, connect an old, dead hd for a load so it will start. If its an ATX supply, you can short the green wire in the ATX connector to a black wire with a paper clip bent into a 'U'. If that doesn't correct the problem, just pitch it but the sparking may be caused by the dust buildup. At least it won't cost anything for you to try!
I've just finished doing the same thing to a computer that had been out in the open in our shop - everything in it was filthy. It had been exposed in our metal fab shop so you can imagine what kind of crud it pulled it. The ps was an ATX but in this old Gateway, the fan pulled air through the ps and blew into the case across the processor. No fan in front so crud was really built up. After cleaning the ps up, I turned the fan around so it blew through the ps and out of the case. That old P-Pro 180 runs fine now.
