Adding 512MB SDRAM: freezes @ logon

Windows 2000 computer with Intel 700+MHz cpu Via chipset
Award Modular bios v6.00PGN 12/21/2000

On bootup the memory count changed, but at logon it just freezes or a physical memory dump error appears.

I added same amount of ram to other workstations and the upgrade worked without failure.

Itried reapiring the OS on 1 workstation, it solved the problem. I tried repairing the OS on another OS with the same specs, at logon it still freezes.

Ady ideas will be greatly appreciated