So is it playing the timeline properly and smoothly with the fx etc...?
I have seen this happen from time to time. My supposition is somehow the key shortcut got remapped so that now, pressing return starts playback rather than render. My solution in the past is to just reboot. You could try the menu drop down for render work area.
Actually...you have a check option in the Preferences
'Play Work Area after Rendering Previews'
I was trying to establish if the OPs timeline actually did render.... or didnt need to be rendered or whatever.