I posted a thread about this problem last week in this thread:
Problem installing MyDefrag 4.1.1
Basically the problem is that after installing some programs, the "All Programs" list in the start menu disappears and is just blank. At the time I thought the problem was only with MyDefrag but today I installed the microsoft Intellitype 6.1 software for my keyboard and the same thing happened. Has anyone else had a similar problem.