Unistall any toolbars you may see in add remove programs.
click start
run
type msconfig
look at the startup folder
I bet you see a couple things in there that don't belong. One may be cnbabe or a toolbar. Uncheck them.
Run adaware, spybot and spysweeper. They are all free downloads. Run each one until it runs clean. Make sure if you have multiple drives, make sure the program is setup to run on all of them.
If you have windows xp you can look at the event log also. It may tell you which program is causing your trouble.
right click on my computer
click manage
click the + next to event viewer
click system and look for errors
double click it and it'll give you an idea of what the errors are
You can also look under application for events.