Vista - Vista Taskbar and notifications area constantly freezes

Am running Vista Business on a Dell Precision WS: 3.73 Ghz CPU, 4 Gb RAM. I
upgraded it from Windows XP (big mistake!). System worked adequatly for about
2 months. Then, the Start, Task, and Notification bar at the bottom of the
screen started to freeze at least every hour. It got so annoying that I had
to write a C# program and attach it to a shortcut to kill and restart the
exlorer.exe process with one click.

A couple of weeks ago, while writing mundane letters in Word, the "Recently
Opened files" list and the "recent opened programs" list and the pinned
"favorite entries" list in the Start menu simply vanished and have not come
back. I have checked The Toolbar and Start Menu Properties, and and all the
pertinent checkboxes and Customize Start Menu choices are correctly set.

I have no idea what to do next. Any help will be appreciated.