I get the impression that G-MANN wants to starts from scratch so lets give what advice we can. It's certainly the most effective way of cleaning out a system and can be very rewarding. I do this at least once every 18 months. Throwing in a bit more ram or adding a new hard drive at the same time gives the PC a new lease on life. Loading on more thisware and thatbot is only going to clutter up a system that G-MANN implies is already cluttered. I think BRL's points 3, 7 and 8 are the most important.
Regards
Stoney