Greetings, please help me resolve this very annoying issue.

Problem Description: On click of Start Menu in WINDOWS XP, the lower half of the menu shows (Programs, Documents, Run, Shut Down, etc), but the top half (I have 6 shortcuts) appears blank, and the entire operating system is temporarily frozen for about 20 seconds. During this frozen period, system will not respond to anything. After 20 seconds, the top half of the start menu appears ok, and everything is back to normal.

Occurrence: occurs occassionally; mostly after long period of not clicking on start menu. I use my computer about 10 hours each day, and this start menu issue happens about 5- 10 times.

What I've done to solve this: downloaded WinBoost, reduced Registry's default startMenu delay value, but this doesn't appear to be the issue.