Agreed, it takes about 10 minutes to figure out a problem with a desktop. Laptop can be a little trickier to fix if you don't know how to open it, not to mention can void any and all warranties with some companies. Although I have never seen a PSU failure or even a HD failure, people say they are common but I have yet to see it, the most common I have seen is failed RAM.
Hard drives are weird things, they fail more often in the first year, settle down for about 3-4 years then the failure rate spikes again, according to Googles research.
PSUs fail because the capacitors can be dodgy, especially in cheap ones, so if the PSU as failed, the likelyhood is that you will find a bulging capacitor.
The other failure relating to capactiors, is the motherboard, Dell have motherboards that are notorius for going BOOM. I had one fail on me, not a problem, £1.50 (about $2.50 or so) for a pack of 10 and a soldering iron (with a really thin point), plenty of flux and desoldering wick, done. I used a complete Pace rework station as I have access to one.
(That would be the dreaded capacitor plauge before you ask, a certain manufacture stole an incomplete electroyte formula, the stuff that makes caps hold their charge, which actually caused the caps to gas inside. The case can only resist the pressure for soo long.)
What wires did your brother cut exactly?
Sounds like the hard drive interface cable to me, very cheap fix, about £1 or $1.60c or so in your money and its plug and play. The graphics card is a seperate component that clips onto the motherboard, my example is here:
EDIT: Or the GPU power cables, he doesn't say and has not post a pic.
As you can see, on my motherboard, the graphcis card fits into an orange slot, which is a PCI-Express (16 lane) slot. Yours maybe different however, as PCI-E is pretty much a PCI slot (the white ones usually) reversed, repositioned and made slightly longer. Although, some PCI slots are also the other way round for compatiblity reasons.
What you probably are talking about, is this:
These connectors on the backplate, go to the IGP and that IGPs are not known for their power or capatibility with games. Mine is a nVidia Geforce 9300IGP chip, so it can play games and it does a good job of that, if only it could cool itself down, as it has a heatsink on the top of the chip, nothing else! You may have an Intel (not as good, but still powerful), VIA, S3 or SiS IGP which are all quite simply, crap.