- Leftover files in system folders / Program Files
- Registry info
- Bad user settings
One tool I have had good luck with is the Windows Installer Cleanup Tool.
Sometimes once you've tried the uninstallers and the cleanup tools, your left with on option, delete the files, and trawl the registry to remove keys.
Editing your registry can harm you pc, backup etc...
The most common places to find applicaiton settings are :
- HKEY_LOCAL_MACHINE\SYSTEM\ CURRENTCONTROLSET\SERVICES
In particular your going to want to look at H
KEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT\CURRENTVERSION\RUN, this is where the startup information is stored, so any apps that start on boot will be in here.