I'm having tons of problems with ram upgrading and i just cant figure out what's the cause. Here's my story:

At first i had 2 Patriot 1gb 800mhz ram sticks. After a while, i bought an OCZ 2gb 800mhz, which caused my computer to freeze regulary.Memtest 86+ didn't find any errors. Later on i found out that the CAS latencies of my old ones and this new one didn't match, so after trying a few more things, i returned the OCZ ones and bought 2 EXACTLY the same sticks as i allready had. After this i had even more problems:

either the computer started without a beep and there would be no display or it started normally and i'd get BSOD often. So i did a memtest for everyone of the sticks (one at a time) and there were no errors yet again. Another weird thing is when i did the tests with the new ram sticks (like i said, one at a time), the computer started normally, but after that when i tried to run it with both of them (but without the old ones) the no display thing happened again.

I really have no idea what to do, so any advice would be much appriciated.

Right. I've found out that apparently my motherboard (ASUS P5K) can have problems with running over 3gb ram @800mhz, so I've set the frequency to 667mhz and my problems are suddenly gone. I'm still wondering though, if there's anyway to make it run @800mhz.

Nevermind the previous post, the real reason was too low ram voltage. I've increased it by 0.2 and the BSODs and freezing are gone.