PLEASE HELP..DISPLAY ARTIFACT WITH NEW HIS 7850

Hello,
i have bought my His 7850 icqx card on 17 the September ..i was using 5770 before.and using catalyst 12.4.
i sold 5770 and bought 7850..installed it

and my problem starts..its strange kind of problem...whenever i boot my pc for first time in day,it shows multi colored lines and dotted screen
no display just screen with colored dots..then i restart my pc and everything works fine....even no problem while gaming..played crysis on maxed out setting..no prob,getin 30 fps on all maxed out

i must tell, u these happens only when i boot my pc first time in a day...like after rest of 3 to 4 hour..then in whole day it works fine.then i shutdown it ,go to sleep and when i boot again same thing happens..i know its kind a strange problem but i am having it since i bought the card...don't know what to do...

so i returned my card,(thought gpu is faulty) and after few days ,RMA department called me saying that my card is working fine on their testing no problem at all ..so they are not going to replace it..they sent me the same card to me

i got my card back yesterday..(it took 8 days to get my card back   )..
i took my cpu to the shop form where i bought my card..they installed card in my pc..and its running fine..its running fine through out the day ..even no artifact on first boot..i was so happy...then again a another night passed and now just half an hour ago i booted my pc and again same exect problem...on boot ,red lines appear and then just screen with colored lines.then no display at all.only black screen...i restarted pc and its again working fine...
now i am really annoyed      

don't know what is causing this problem...what should i do now..??RMA guys is not going to believe about the problem ..previously i called them and explain them what kind of problem i was having and they are keep saying that hey hadn't acquired the kind of problem on there testing...now what to do ?????
please help.....

my specs are
Gigabyte mobo --GA 880GM UD2H..(REV 1.4).BIOS ver F8(letest)
Amd phenom 2- X4 965, 3.40 ghz
His icq x 2 gb ddr5 7850
Windows 7 home perimium 64 bit
Corsair thx 650 watt psu
4 GB of RAM.2 stick of 2GB one corsair ,,one kingstone
and at present using catalyst 12.8.((had tried clean install of amd driver several time)no luck with it

lots of thanx in advance......