Graphics Grief?

Hi all.
I have a Radeon 9550 256mb card.
I get lock up when online gaming. MOHAA.
I have swapped my card for another identical card from a mates comp.
This one is even worse.
It crashes almost immediately leaving a blank black screen.
I restarted and didn't even get online before the screen became a mass of colour.
The fact that I have tried two identical cards and got such different results has me more confused.
I have the latest drivers installed so the cards surely should act the same??
One other thing, I have a single beep on start up, not the POST beep but a beep just as the welcome screen is loading?
My motherboard manual points to a refresh error?
Any clues anyone?
Cheers.