After Effects preview won't play all the way

I have been using AE for a few months and I haven't had a problem like this before. The green line will form and the time indicator will only play until the end of it-- about 2 seconds long. If I move it forward, it will play a little longer but ultimately it wont play my entire comp. Even if there's literally nothing dragged in, it'll do the same thing. I've tried purging my disk cache and I have 4 GB of RAM allocated to AE (I've tried going up to 7 GB, doesn't work either). I've tried experimenting with the different resolution options (quarter, third, etc.) but it plays for the same amount of time. Honestly, I used to have about 65-70 GB of storage and AE used to work just fine, so I wouldn't get if storage was an issue. 

Any help is appreciated, thanks so much!