Upgraded to 10.9, but it broke my Windows 8.1 Boot Camp partition!
You could try to fix the MBR Table.

I would recommend by using a Linux LiveCD or the rEFInd CD http://www.rodsbooks.com/refind/index.html

Alternatively, rEFInd can be installed on OS X so you also get a Partition Manager Tool. I used this tool once to fix my broken MBR Table.

You can find the install instructions for OS X here: rEFInd Install OS X

I hope this helps.