iMac G5 problems?

Okay, so two weeks ago I come in and my iMac is acting weird (iSight G5, rev c. 17" with standard RAM because Crucial hasn't arrived yet). By weird I mean the fonts are skewed, I cannot open programs and if they do open they all go white. Finder is messed up and won't load certain folders. I cannot open Preferences either. So, I reboot a few times and it still does this and when I would get to the login screen it would be all scrambled but I could login by typing my password and it would go back to the messed up desktop. I reinstall OS X (Tiger) and then update. Now, two weeks later I keep getting the White/Grey Screen of Death (You must Reboot your computeR) every so often (every two days) and the computer crashes a lot. Tonight I get back upstairs after about three point five hours of making bread and watching television and the screen is black and will not respond and the fans are running non-stop!

So, I re-boot and I would like to know wtf is the problem? Do I need to get a new iMac or something? I was not even running anything when I left it but Firefox with four tabs and Zudeo (Azureus) with two torrents. This started happening (White/grey screen) a month after I first bought it (Jan 06'). Silly me, it was a gift and I could not afford AppleCare at the time so I never got it. X_X

What can I do? I bought this computer in December 05' and now it decides to mess up. Will the ram help? Is this a Kernel problem?

Good news is I'm waiting on my MB to ship out, but with the iMac problems I'm considering returning it and just going back to PC (ugh) and finding something to do with this iMac...

Any ideas?

Cross posted on Mac Forums (.com)

Yep, it did this after the install. The install didn't want to load the first time so I had to re-boot the first time I popped it in.

Never having done that, how would I check and run all those from the install DVDs?

I hear that if Apple cannot solve problems with hardware after 3-4 times they will replace the system, if that happens is there a good chance they have PPCs still around? I am not a big intel fan X_X. Save for the MB.

EDIT: After seeing how to reset the SMU, turns out I've done that and still the issues.

Update:

Okay, it is doing the weird fan thing again tonight/this morning. Damn! And before my external HD gets here so I can back everything up. The thing is it will not turn on really. The light comes on, it chimes, and then the fans start running fast but the screen stays black. I can do nothing on it except charge my iPod. And what is worse is I turned off file sharing on it this morning I think. Other wise I could access it from my mac book :[[.

Any ideas?