Similar problem ,, different video cards check psu GTX 450 should have at least 600w psu [??]...I use OCZ Stealth X Stream because they can deliver 700w even though they are rated at 600w, check the review at Hardwaresecrets.com...:)
Post facts with statements like that! The below is borrowed from EVGA for GTS450 it is total available system power req.
Minimum of a 400 Watt power supply.
(Minimum recommended power supply with +12 Volt current rating of 22 Amps.) "http://www.evga.com/products/moreinfo.asp?pn=01G-P3-1450-TR&pwindow=specs&family=&sw=
Total system load with GTS450 running Furmark 270watt http://www.anandtech.com/show/4221/nvidias-gtx-550-ti-coming-up-short-at-150/16