I would suggest that you have been infected with viruses or spyware and your protection software has deleted the beasts but startup traces have been left behind. You could try a fix by going to Start then Run. Now type in 'msconfig' without the quotes. Open the Startup Tab. Scroll down the list and untick anything relating to your problem. Now click apply, click ok. Re-boot your computer. Eventually when your computer boots you will be presented with a new pop-up window - tick do not show again.
To get rid of any remaining infections -
Free - For starters, download, update and run a full scan using SuperAntiSpyware (SAS) http://www.superantispyware.com/
SAS is an exceptionally easy to use application that will remove the majority of difficult Trojans and Worms, not just the easy ones. In addition it has the ability to remove Vundo and Smitfraud infections. SAS can lock your home page to prevent browser hi-jacking attempts.
If possible it is recommended that you load SAS in normal mode but run it in Safe Mode. Safe Mode can be started by continually pressing F8 during the boot sequence. If you are badly infected you might need to run SAS more than once to help clean your system. Afterwards if the only infections now being shown are in System Restore, once you are completely satisfied that you can boot normally, you can either delete the infected restore points manually, or temporarily turn off System Restore to purge the files.
Assuming you have some real awkward infections that persist even after trying all the above I suggest you download a dedicated Smitfraud removal program from:
http://www.afterdawn.com/software/desktop_software/desktop_security/smitfraudfix.cfm
If possible run in Safe Mode.
Likewise the dedicated VundoFix:
http://vundofix.atribune.org/
Good luck & safe surfing.
wdw