text: In all likelihood, while mcafee WAS the latest thing you installed on your computer, it is NOT the problem keeping your computer from booting correctly.  When you say, it won't let the computer boot up, what exactly does that entail?  Will the computer not turn on at all?  Or does it give you an error?  If you can't get into windows itself, you'll have to go through DOS itself.  Use a boot disk and get into dos.  Run chkdsk to make sure your file system is not corrupted and possibly try a defrag.  If it really was Mcafee (which is highly unlikely) call their support line.  They will definitely give you some good advice on what to do and if it is their fault, they will probably refund/reimburse you for your troubles.