I am assuming he meant doing a repair of the OS. It can be done, but your BiL is full of horse pucky.
"Having trouble"... such as? Unless it is Windows itself causing trouble, you shouldn't have to worry about a reinstall/repair. If it is something else, we can help you fix it.
What kind of system maintenance do you do on your machine, such as spyware/adware scans? Anti-virus? Defragmentation? Cleaning the registry? Deleting temp files? Cleaning up the startup?