Performance degraded over time

Hi everyone,

I've just purchased a Powercolor HD4850 PLAY!. play a few games like crysis, the last remnant,cod4,medal of honor airborne etc. those games run great and smooth. after hours playing i noticed my hd4850 performance degrading over time. 2 weeks later i found the exact same games run terribly lag during intense graphic even right after booting pc..i think heat is not an issue here.so am i getting..

1) defective PSU caused by too much load?

or

2) permanently damaged card(too bad to be true)

i have a crappy no-name 390W PSU.20a(max) on 12v rail.
c2d e6550@stock
mushkin 2x1gb 667mhz
asus p5n-mx
western digital 320gb
samsung dvd-rw writemaster

btw sorry for my bad english!

You`re really pushing your luck with that PSU, and it`s by far the most likely hardware problem. Look to about 500W from a good supplier such as Corsair, OCZ, Pc Power and Cooling or Antec.
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thanks for the reply. i got few bucks here to spend with. which one is good decent psu?coolermaster extreme powerplus 500w or vantec ion2 450w?i need some time to get those expensive high-quality psu such as antec,tagan,ocz,corsair etc.as 4850 uses only 110watts@full load,e6550@stock clock,single hard disk,2x667mhz ddr2,a 120mm 12v 0.3A and 2x80mm 12v 0.18A,my biggest concern here are noise and ripple produced by psu.continuous 20-25A on 12v rail probably way more than enough for my build.at this rate which psu can deliver low noise and ripple(estimation 40-60mV on 12v rail @intense graphic) for $55-70?i will get a tagan soon once this wallet grow up little bit heavier..