HP Notebook low resolution

Archived from groups: comp.sys.laptops (More info?)

HP Pavilion Notebook ZT1150
WinXP SP2 (upgraded from SP1 in the summer)
768 MB RAM (512 + 256)
S3 VIA Twister display chip - S3 Graphics Twister HP driver

After starting up recently, my monitor resolution was stuck at 640 x 480
and 4-bit color. The Advanced Display menus that let me change the
amount of VRAM had disappeared. Sometimes reverting to older System
Restore Points got the resolution and color back to normal, sometimes
not.

When the Restore didn't work, I took out the 512 MB RAM module (which I
purchased five months ago). The monitor filled out fine with just the
original 256 MB module. With the VRAM at 16 MB, I re-inserted the 512
MB chip. The monitor works fine this way. But if I change the VRAM
from 16 to 32 MB (the maximum), the 640 x 480 4-bit problem comes around
again.

I'm running Windows Memory Diagnostic right now and so far on Pass 4 of
the 512 MB chip only, no errors have been found. The 256 MB chip had no
errors on two passes. Should I run the extended tests?

I have RAM Cleaner installed, but I set the preferences so it doesn't
run all that often. Could that program be the problem?

The video driver I had installed was the latest and had been working
fine (Microsoft S3 Driver). I reverted back to the original driver from
the HP Recovery Disks, but the problem seems to occur with both drivers.

About the RAM: I purchased a 512 MB chip from a certain online company.
It was shown to be defective after running memory tests, so they sent me
a replacement module, the one I have now. It had been running fine
since July with the VRAM set to 32 MB.

Any suggestions would be appreciated.