1. well since you did have restore point before installing bittorrent, then restore back to that point in time, unless computer tells you it can't do that.
2. check your computer with anti spyware and anti virus program(s)
3. if you have done above and you are you have clean system, then try resetting the default programs used to run files on default (like music player, default browser, etc) and checking other settings that you think might have affected what programs open what things.
4. if nothing work, then back up all important files / files you want to save, make list of all software you will need to reinstall, then reinstall windows or boot recovery cd, or use recovery program.
If you have HP or compaq computer, then you most likely have recovery program on computer already installed by manufacturer, so just run upon rebooting by pressing correct keys and following directions.