Sometimes, you will find that the uninstall program leaves bits behind - the worse ones are those that leave entries in Windows registry or in the start-up. You need to delete these manually, (although, if you've got Norton Systemworks, the System Doctor could solve this for you).
First go to <Start><Run> and run a program <msconfig>. Use the rightmost tab, which will bring up a list of all programs loading at start-up. Check the list and uncheck every mention of the program you have deleted, if any. You will have to reboot to check. If you still have problems, check all copies of a folder called Startup on you C:\ drive and set if there are any icons for the program and delete them. You can now try another reboot. If you still have problems, you will have to remove them from your registry. Having first backed up your registy in case of problems, go to <Start><Run> and run a program <regedit>. Search and delete EVERY entry (and there could be many of them) which refers to the program - or to its manufacturer. For example, if you want to delete Notron, you will have to search for Norton AND Symantec - they don't like to let go.