I have a dell optiplex gx520 with xp pro the computer will shut down and the power light will blink yellow I have to unplug for about 30 sec and it will start up as normal but in about a hour it will go back in that mode help????

before I tell you to open the case , is it still under warranty? larry

See Diagnostic Lights, and Diagnostic Leds, on this page: http://support.dell.com/support/edo... There are three different cases this model series can be in. Click on "Back to Contents page" at the top of the page for specific manuals for the model you have. Probably the most likely thing is your power supply has started to fail - failing mboards are relatively rare. You could try making sure everything inside the case is properly seated, etc., but failing power supplies are common. Check your PS. See response 4 in this: http://www.computing.net/hardware/w... If your case is the largest (and widest) of the three possible, you can probably use any decent standard sized standard ATX PS as a replacement, that has the same wattage capacity or greater. Standard (PS/2) power supply size - 86mm high, 150mm wide, 140mm deep, or 3 3/8" h x 5 7/8" w x 5 1/2" d , or very close to that, though the depth can be more or less for some PSs. If your case is one of the two slim desktop models, you probably have an oddball sized PS box (that has standard ATX wiring), and a replacment will either have to be the Dell one, or a clone that you find when you search using the Dell part number on the PS. Don't buy an el-cheapo PS. See response 3 in this: http://www.computing.net/answers/ha... .......... Important - but ONLY if you have a graphics card in a mboard slot: Your power supply must have at least the minumum capacity required to support a system with the graphics card you are using installed, or the max graphics card you might install in the future. (Onboard video - video built into the mboard - IS NOT A CARD!) You can go to the video card maker's web site and look up the specs for the model - often under system requirements - the minimum PS wattage, and, more important, the minimum amperage the PS must supply at 12v is stated. If you don't find that, any card with the same video chipset including any letters after the model number has very similar minimum PS requirements. If you want to cover any possible video card, a minimum 600 ot 650 watt power supply will handle any current high end video card, or even a X2 card (two video chipsets on one card) or two cards in two slots.