Once the logic board

was installed, my system ran like a champ and had no boot problems, they had 1 stck of memory (weird because i have 2), and a new 320 gig hard drive, which i had to give them something in return for them to turn back into apple.
it ran great for a bout a minute.... then
as i put the computer to sleep, it sounded as though it woke up, but nothing showed up on the monitor, AND...
(known issue that apple is awhare of with my computer)
once the OS loaded up my mouse froze, and i got a blue screen (like the one you get right before it shows your account logon)... it stayed blue for about 5-7 seconds then went away, I have had this issue before the logic board was replaced, and now obviuosly after,
every thing looks to be good except these 2 issues?
the tech said it could either be my memory, my OS, or my video card?
ANY SUGGESTIONS?
i am going to be calling apple again to tell them that i am still getting the blue screen from time to time, and i can still type and everything, but all you see is a blue screen...then it goes away,
it even does it when i boot into the apple hardware test, or off of the dvd OS,
Any suggestions?