I had just added a new keyboard to a Dell desktop

This could be coincidental but there are some things you can try. First of all turn off the computer and remove the battery. Then remove the hard drive and re-seat it. If this doesn't work then you need to have the HDD checked out to make sure it's bad (which is most likely is). You probably need a new hard drive but these are the steps to make sure. Feel free to check out www.inovagent.com if you need help.

1. It happen to me one time with my acer aspire, but since the warranty of life top expired already, what I deed is that I open up the back where my hard disk is located, I just remove it and and after 5 mionutes re-attached it again then i turn on the laptop and it works again.

this is only advisable if you know how to access your hard disk and if it's warranty is lapsed already.