Heating Issues with Nvidia BFG 9800 GT qgb

so i just finished building my new budget gaming pc, and i was playing around with it for alittle bit. I downloaded TF2, and when i went to play it , as soon as i joined a match, the whole system restarts, then it restarts again and again. I shut it down, and think i'm just tired and crazy. I come back the next day, install fanspeed, and see that when i start TF2 or Neverwinter Nights 2, the GPU goes from around 48 degrees Celsius, to around 70 and up. I'm still not sure why that is resetting the system, Because i went into maintenance and made sure auto reset was off. Does this happen to other computers when the GPU overheats? Is my card defective or do i just need bette air flow? ( I have 5 fans in the case 2 -120s and 3 -80s). I even brought the computer down to the cold basement and it still reset, I'm stumped, i read reviews saying the card ran hot, but not saying that it ran hot enough to restart the system every couple seconds.
Any suggestions or diagnoses would be GREATLY appreciated
o rite
my build (if this helps at all):
case-RAIDMAX AZTEC ATX-619WUP Black/ Blue SECC Steel ATX Mid Tower Computer Case 500W Power Supply - Retail

GPU-BFG Tech BFGE981024GTOCE GeForce 9800 GT OC 1GB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card ... - Retail

Processor-AMD Phenom II X4 940 Deneb 3.0GHz Socket AM2+ 125W Quad-Core Black Edition Processor Model HDZ940XCGIBOX - Retail

Motherboard-GIGABYTE GA-MA790X-UD4P AM3/AM2+/AM2 AMD 790X ATX AMD Motherboard - Retail

Memory-CORSAIR 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model TWIN2X4096-6400C5 - Retail

Hard Drive-Seagate - Barracuda 1TB Internal Serial ATA Hard Drive

^+1

someone should make a sticky on PSU tiers

Its likely because of the POS power supply, assuming raidmax uses their own PSUs in their cases then it has to be this one
http://www.raidmax.com/specs/RX500SB.html
With only 22 amps of current available from 12 volt sources it gets beaten by an antec EA380 PSU that can provide 27 amps on its 12 volt rails.
http://www.newegg.com/Product/Prod [...] &Tpk=EA380

Now i tried the radeon x1600 512 and after around an hour of playing neverwinter nights 2 , it reset. When we opened the case and checked the card, it basically burned to the touch. Also, if the problem was the power source, wouldn't i see signs of the power source being overworked? When i checked it, it was not very hot, and there was no smoke or anything.

If the PSU even felt warm it was hot by PSU standards, hot to a person is about 150F which is about 65C which is way too hot for the PSU. If it even felt warm then it was probably too hot, if its below your body temperature it will feel slightly cool to you so any metal below about 37C feels cool so if it feels warm its rather toasty for the components in there.