ssd - Hard Drive got assigned letter F and boot fails

I cloned a partition from my old drive and installed a new SSD in my laptop. But now when I go to boot, after I log in, I get the message "preparing your desktop" which never finishes. I have no start button, nothing. Except that I can start task manager. There I see that my hard drive is now assigned to F, not C and thus will not boot. When I try to run diskpart to change the assignment, it says that diskpart cannot be found, even though I see it right there.

Any ideas? I really do not want to start over with a clean install.

Thanks.

Windows 7, 64 bit