Boot up holding command-r keys into your Recovery Volume.
The screen should give you these choices...
Restore from TM backup
Reinstall Mac OS X
Get help online
First run Disk Utility > Repair Disk and see what it reports... if there are problems run until repaired or states it cannot be repaired. Then,
choose Reinstall OS X. This will be an install in place and won't affect any of your own data.