Network makes computer shut down

yes, i made a new computer last night and installed sp2 and all the other ogod stuff from a disk. Works GREAT. BUT, when i go to the internet surfing isn't too bad (as in it doesn't restart that often) but when i update the steam platform the computer shuts down! over and over agian almost at the same update percentage it shuts down. its a an8 sli mobo with integrated gigabit lan card.

x2 3800
2*512 ddr 400 pc 3200
geforce 7600gt
xp pro sp2
160 gb sata 3.0 hd
burner

ANY suggestions??? would be very helpful
AND most if not all the drivers have been updated.

naw temps are fine 21 fer cpu, 26system, 30 for power. but yeah i uninstalled the firmware/wire (?) and i said to not install the added firewall from nvidida and that fixed it...works perfect now.tx