After almost one week without being able to view my hotmail, I figured out the problem.
I noticed the date of the first unread message I couldn't open and saw that it was the same day I installed the latest vDownloader... I uninstalled it and now everything is back to normal.
If you are having problems check whether you installed any new software recently.
Hope I have helped,
I am having this problem too, only as of about the 23rd-25th of may dun remember exactly when. I did safe mode first.. than cleared cache and cookies (well all the "clear" options). both tests I had the same problem