7800 gtx 512mb probs...help!

[tartanmadman01]

hi guys and girls..just joined forum and hope you can help me........
i have a 2 month old xfx 7800 gtx xxx edition 512mb from ocuk in my 4 month old compaq presario machine........
amd athlon 64 processor 3700+,1gb ddr,320gb,256mb video mem,450 jeantech power supply and a 19" xerox tft flat monitor(1280x1024)).
the prob is that i am getting severe artifacting and distortion on bf2, farcry, quake 4, fear etc.
I have had this problem from nearly the first couple of weeks and have had to play the games in low to medium setting to get anywhere(not the reason i bought the card for).
Should i 1.. be able to play my games with maximum on and all the toys with this card in my machine? and 2 if so a card prob????.
there is no overheating prob as the temp stays at 42/46 and i have downloaded the latest drivers.
I have had the computer checked at a leading computer store were i bought the machine and everything is tip top and fine.
I have rma,d the card and sent it to ocuk for testing but if they send it back to me telling me the card is fine as they have done with other customers then what should or can i do.
Any tips or suggestions would be most welcome to a new member..
kindest regards folks

 

[tartanmadman01]

thanks for a quick reply.....when you say my psu isnt up too it do you mean my machine..

 

[tartanmadman01]

Thanks....the so called competitor has mysteriously vanished??...
When i got the card installed they fitted the 450w power supply as the exsisting one was only 350w??

 

[tartanmadman01]

thanks for your help guys and girls....does anyone else out there have any ideas what else it could be...spoke to someone about power supply and they assured me that the 450w psu is adiquate even though the card is a bit power hungry!