Today when I opened up my project the play function doesn't work in the timeline. Whenever I press the spacebar or the L key, the playline indicator goes to tthe start of the sequence. I have tried this on different sequences and projects. It will play on the source side fine. but not when the timeline is activated. My keyboard commands are the same.  I've been editing on the same system for 6yrs so doubt it has anything to do with specs. This is the latest version of MC. I have transcoded the timeline from the AMA clips and still get the same result. Any help would be greatly appericated. 

Try a new user setting. If the problem goes away, your old user settings are the cause.