What is wrong with my computer?

I have a Toshiba, working with Windows Vista Home Premium. Until now it has worked accordingly for all my graphic design works, just about everything was normal. Since about two days ago, MS Paint and Notepad won't work. They don't open any files, or open on its own, they simply don't work. I have not downloaded anything recently, and I have not received any notifications of a virus. This is small, but minor things like the "switch between windows" on the task bar looks different now and windows take a while to open. Not only that but when turning on my computer it takes me several tries for it to actually start. I have lots of work to get done in which I need these two applications. What is wrong and what should I do? Please help.