how can I get my screen resolution back to normal?

My screen resolution stays on low bit 4,
when I move the slider to the normal position,
click Apply, it moves back down to 4 again.
All my desktop icons, games and Internet
windows are very pale colour, windows
have many dots in them which's very
difficult to look at.

I've tried downloading drivers and 1 didn't
complete yet it said it was 'safe!' The
others take far too long which uses my
Fair Use Policy (FUP) and with T-Mobile
Internet it goes very quickly, I can't go on
the Internet at all most of the time.

I also need help with my sound driver too.

My home PC's:

COMPAQ 2.4 40GB HDD DVD-RW XP PRO with
no system CD-ROM and Floppy disks, I bought
it second hand and didn't have any trouble until
recently.

Thanks