|"the powersupply is fins so far..."|
Sorry, the PSU is a cheap piece of crap. Does it have a single +12v rail or multiple +12v rails? If it's a single, is it at least 30A? If it's multiple, does each +12v rail have 18-20A? What about the +5v rail? Closer to 20A or 40A? PSU manufacturer's fudge the wattage rating by loading up on the +5v rail. The difference between 20A & 40A on the +5v is 100W. Do you know what uses the +5v rail? Not much. My guess is your PSU is at best, a 400W unit, but it doesn't have enough amperage on the +12v rail to power your higher end/power hungry hardware.
Look at the amperage specs to the PSU that I posted a link to:
+3.3v @ 30A
+5v @ 20A
+12v @ 41A
My guess is your PSU specs are something like this:
+3.3v @ 30A
+5v @ 40A
+12v @ 20A
Check the label.
Do you know the power requirements for the 9800GT? Minimum 400W PSU with a minimum 24A on the +12v rail. Hmmmm.
Besides the PSU, how did you go about applying the Arctic Silver? Another question might be WHY did you use Arctic Silver? Regardless, here's how it should have been applied...if you did it any other way, remove the heatsink, clean it, clean all the paste off the CPU, then do it right: