Computer has changed overnight, Desktop not found.

When I started up my computer this morning, I discovered my windows theme had reverted to a Windows Classic-style theme and my desktop background was a solid black. There are now no icons on my desktop except a recycle bin. Looking in the C: drive shows the files are all there but I cannot access them.

I get a popup saying
"C:\Windows\system32\config\systemprofile\Desktop refers to a location that is unavailable. It could be on a hard drive on this computer, or on a network. Check to make sure that the disk is properly inserted, or that you are connnected to the internet or your network, and then try again. If it still cannot be located, the information might have been moved to a different location."

The only thing that has changed recently since I last used the computer is that there was a windows update.

Tews said:

Try doing a system restore to a point before you ran windows update..

How would I do this? I've never done a system restore before and I cannot access the majority of the computer right now

Work through the steps for Troubleshooting Windows 7 Failure to Start