Suggest you download and install process explorer from:
Process Explorer
It gives you a much better overview of what's running than task manager. You can tell it to open when you use <ctrl+alt+del>
The other thing is to look in the start-up area ( type ' msconfig ' in the run box) and untick all non essential programs, if the problem goes away then re-enable them one at a time until you find the one that causes the problem. If none of them cause the problem then look at your apps one at a time, unfortunately it's a slow process as you need to let each simmer for awhile it could also be the anti-virus software slowing you down after an update.