Here's a search for articles on that: https://www.google.com/#q=screenshot+with+dropbox

Let me share that I did run into 2 PCs that hung like yours. Both had malware infections, one had Norton the other McAfee. So after a full backup image of the HDD was made since a lot of malware is now booby trapped we used Grif's advice at http://www.cnet.com/forums/discussions/how-to-remove-pup-option-603542/#post-f742c795-5881-433b-a29b-6d758efe5cd3 to remove the malware and finally uninstall the antivirus suites since those can interfere.

I'm not sure but suspect that CD/DVD drive emulators can interfere so those are remove along with torrent software.

So far that has fixed a few first hand and by reports from others, many others as well.

The key step is to have a full backup in case of a really nasty infection.

--> Almost forgot. Unplug things like printers, phones, scanners, USB memory/drives and such during such an upgrade.