Computer slows down and issues on opening windows programs

Hi folks,
It's been like this for so many days now. For about 10 mins after starting windows, when I right click my desktop, my mouse pointer stays in "waiting" icon. Not only that, my computer slows down drastically and I notice I cannot run windows built in programs like task manager, regedit, msconfig etc.
What's causing this?
How can I fix this?
Thanks for your help.
