vertical bars appear on display

hello everyone

i have a sapphire 9500 (128mb)

The problems I am having are intermittent but result in me having to restart
my computer. Every now and then (probably once every 3 uses of my pc) I get
white vertical bands on my display. They are about 1 inch thick and are
about 1 inch apart. They go across the whole display. I cannot see through
them. I run my system at agp 8x, 85hz, 1024x768 and with 32 bit colours.
When the fault occurs I sometimes rectify it by altering the resolution.
Sometimes it works but sometimes it doesn't. The computer works fine when
the error occurs ie. the pointer still works as though the bars arent there.
I have tried installing the latest drivers off the website including the
control panel but it doesn't make any difference and have installed old
catalysts 3.5 drivers as well but that didn't help either.

I haven't overclocked any part of my system. Do you think my card might be
faulty or is it something else. i have run the virus checker and it didnt
find anything.

Thanks in advance

Matthew