64-bit bios Asus P6T

5 gb of ram??? let me guess, you installed 2x2 gb and 1x1gb? or maybe 1x2gb and 3x1gb?

You're better off having all ram slots having the same capacity of ram, that might clear up your problem.

If that's not the answer then check your Ram settings in your bios.

physical address extension on the mobo might need to be switched on, aka memory remapping?

Check to see if "OS Install Mode" is on in BIOS.

Not sure how to memory remap but i did replace my board with an XFX x58i turns out my P6T had a Bent back and curled pin figures might have been when i had one of my brothers friends try to fix it first time it crashed.