Sounds like possibly a windows permissions issue, especially if the entire web viewer is an issue (as opposed to a broken page inside the web viewer area).
If the only variable is user account I would start there. Have the IT guys compare your permissions vs. a standard user's. Maybe clone a working user's account and set it up for you?
We are watching strange webviewer behavier in combination with FM 13, Internet Explorer 11 and Adober Reader (latest version).
After switching back to IE10, most problems are solved. I'm not sure aber the Adobe Reader, but this is updated constantly. This might also help in your case.
Turns out that re-setting my local profile solved the issue. This has happened with others in our office as well. There must be a conflict or it's just a fm13 bug.