If you have upgraded to Windows 8.1, you are now using Internet Explorer 11. OWA (from Exchange 2007, 2010 or even the new 2013) does not work properly with IE11 does not work in full mode.
UPDATE: January 2014
This problem should be resolved in:
- UPDATE ROLLUP 3 FOR SERVICE PACK 3 for EXCHANGE 2010
- CUMULATIVE UPDATE 3 for EXCHANGE 2013
My experience with UPDATE ROLLUP 3 FOR SERVICE PACK 3 for EXCHANGE 2010 is that it is still not working but see ROLLUP 4 is ready sooooo, lets hope it is in there.
Alternately, you can add your OWA site to COMPATABILITY MODE.
Microsoft is aware of the issue and is working on it. As a work around you need to: Launch Internet Explorer 11 Press CNTL + SHIFT + P This will start “In Private Browsing” and when you use IE11 with In Private Browsing, OWA will operate as normal.
This Microsoft OWA article provides more explaination if you need it.