USB DEVICES PROBLEM WITH WINDOWS XP SP3!!!

Hi,

I have Windows xp sp3 on Intel D845gvsr+512mb ram+intel pentium 4-2.4ghz.

My problem is that windows xp sp3 is detecting my USB pen drives as
Unknown devices whereas those drives are working fine on other computers
with comparably same specs.
I tried following:
1: Fresh installed windows xp sp3.
2: Installed video,audio, intel inf drivers.

Then plugged in my usb pen drive but it is still being detected as
- Unknown device.

My whole system is otherwise working fine, no problem with other NON-USB
devices on system but this USB DEVICES thing is just making me crazy.

Plz help me thoroughly as I can not afford to change my system.

Waiting in positive expectation.

Regards.

Oc9ine.