Try the obvious, unlikely to fix it but:
Restart steam, restart pc, verify game cache on steam etc.
If that doesn't work, you have the most annoying problem on steam that most people don't really how to resolve... I once had too.
So the next best thing is to go to Program Files\Steam\steamapps\common\Football Manager 2013 and run fm.exe as Administrator (right click)
+ running steam as administrator could also help.
If that doesn't work... You stop playing FM13 for 2 days, turn on the computer one day, and it magically works... That happened to me.