Question : Problem: Onboard graphics card failing, how do I replace?

Hi my son is having a major problem and I hope someone here can help me before having to resort to paying a computer tech to fix it. His graphics card is going faulty, the agp slot is no longer picking up his monitor, we thought it was the monitor but after trying several monitors we realized it was the actual AGP port that was not working. I believe he has an onboard graphics card. I dont know what to do. Do I replace the onboard card? the entire motherboard? or can I just buy a new graphics card and disable the onboard one? Here is a link to see the computer specifications so you can better understand what I am dealing with. Thanks for any help you can give me.

http://www.shopping.com/xPF-Gateway-Gateway-GT5058-Desktop-PC

Answer : Problem: Onboard graphics card failing, how do I replace?

Make sure he reads the sticker on the side of the PSU and gives you the "positive 12 volt amperage rating for the PSU. It should be at least 22 amps(good overhead) if there is only one 12volt rail .
It may have two 12 volt and will be indicated as such with 12volt 1 and 12volt 2. The Amps can be combined from these two rails like 16Amp and 16Amp would give a 32Amp rating,(may not provide the full 32Amps but you get the idea)
here is a list of trusted PSU's and just below it " Some Not Recommended Power Supply Makers"
http://www.overclockers.com.au/wiki/Power_Supply_Unit#Trusted_Power_Supply_Makers

Here is an example of a PSU spec sticker that has one +12V rail @max 23Amps
http://www.jacobmp.dk/media/freeze60/psu_stats.JPG

Here is one with two +12v rails (+12V1 @ 20Amps) ( +12V2 @14Amps)
http://www.hardwarelogic.com/articles/reviews/PSU/SeasonicS12-330W/SeasonicS12-330W_SpecificationSticker.jpg