If you try and access the start bar straight after logging on, it might just be that the PC needs time to boot up all the necessary drivers and software. My PC needs about 2 minutes to fully boot up, even though it looks ready in 5 seconds. Check if your CPU is working over 40% when you're trying to access the start bar (using something like CoreTemp) - if it is, then the PC might just be booting software and you just need to give it a minute. If not, then it may be an OS file corruption of some sort and a reformat might fix it.
I agree that we need to know your PC specifications to help you out further. Are you using Vista or XP? Single core or Dual core CPU? RAM?
EDIT: You say some of the background programs dont show up in the task bar - why not exit them using the Task Manager? Windows tends to hide some of the icons in the task bar whenever it feels like it :P
AG