Is this a virus? Taskbar has gone!

[T]

My computer running XP Professional suffered a sudden slow down and the
Taskbar shrank is size. After a reboot the Taskbar disappeared. It is not
hidden as the start menu does not respond to the Windows Flag key.

I reformatted the drive only to have the same problem reoccur a day later.
I reloaded using the original media which I have successfully used before.
I did however use fresh copies of Avast Anti Virus and Zonealarm downloaded
with another PC and scanned with Avast which indicated that they are both
clean.

The only explanation I can think of is a boot sector virus. Is this
possible after the disc was reformatted and is their a way I can know for
sure? Is there a way to wipe the boot sector completely. Avast insists
that the PC is clean.

Thanks.

 

[Bruno]

My computer running XP Professional suffered a sudden slow down
and the Taskbar shrank is size. After a reboot the Taskbar
disappeared. It is not hidden as the start menu does not respond
to the Windows Flag key.

I reformatted the drive only to have the same problem reoccur a
day later. I reloaded using the original media which I have
successfully used before.

Did you *boot* from the original *CD*? Did you password protect the
Administrator account after installing Windows?

I did however use fresh copies of Avast Anti Virus and Zonealarm
downloaded with another PC and scanned with Avast which indicated
that they are both clean.

The only explanation I can think of is a boot sector virus.
Is this possible after the disc was reformatted and is their a way
I can know for sure?
Is there a way to wipe the boot sector completely.

FixBoot (Recovery Console) overwrites the boot sector, and FixMBR overwrites
the first 460 bytes of the Master Boot Record.

Avast insists that the PC is clean.

It might not be a virus.