Explorer doesn't display text, taskbar, or windows

I recently booted my computer (details below), and the only things that were
displayed when it logged on were the icons on my desktop, my desktop
background, and any images associated with programs that popped up (eg. gmail
notifier logon prompt background). I could still access task manager (the
Ctrl + Alt + Del menu worked fine), but task manager did not display anything
but white rectangles. The computer is still technically funcitonal, but is
not usable. I am assuming that all programs run and work. I have power-cycled
three times, with the same problems. I cannot enter Safe Mode.

COMPUTER DETAILS
-Acer Travelmate 6292
http://www.cnet.com.au/laptops/lapto...9278556,00.htm
-Windows XP Professional 32-bit
-Belongs to school network, has worked fine previously
-Accesses wireless internet from home
-Sophos Anti-Virus software installed and operational
-No major software or hardware changes recently

A solution to this problem would be greatly appreciated.

Thanks for your time and help,
Bill Connor