Vista - Deleted Icons re-appear on Desktop

Hi I'm a newbie her, so apologies if someone has already asked. I'm Vista
Ultimate on a Core 2 Duo PC, 2GB RAM , 350GB Hdd.
I have a problem where periodically any deleted icons or files from either
my desktop or quick launch bar re-appear. For example I have a bunch of PDF
files on my desktop I don't need anymore, I dragged the files into the
recycle bin, then emptied the recycle bin, refreshed the desktop and kept on
working. A few hours later they are all back again. I can open the pdf files
and the all appear as they did the day they were created. I wasn't doing
anything weird for them to come back, just checking emails, working on
database on my pc and paying bills etc. Also any icon from an old program
re-appear, programs have been uninstalled long ago, but the icons keep coming
back. Doesn't matter what I try they keep coming back. Sometimes after a few
days and reboots other times only after a few hours. I've never seen anything
like it before in my years of using PC's Any help would be greatly
appreciated.....