Playback issues

I have seen this issue on a couple other threads in this site, but none of them provided a definitive answer, so I created an account and decided to ask myself. I start up Pro Tools, and work just like normal. But then at some point, Pro Tools decides to quit doing playback. It won't cut out in the middle of playback. What happens is I press spacebar to play, and the the stop button will flash blue simultaneously with the play button flashing green (kind of what it looks like if you right click the play button and choose 'prime for playback'). I also notice that Pro Tools seems to be running rather sluggishly, and it takes the software longer to close than normal (once it took up to ten minutes). This phenomenon happens on both small (The smallest one was simply one mono audio track with nothing on it) and large projects. There is also no obvious correlation between anything I do to link this phenomenon. I also had this problem with Pro Tools 11 (I am running 12 now).
A few details about my setup:
Computer: HP Envy - (Intel(R) Core(TM) i7-4700MQ processor @ 2.40Ghz; 12.0 GB of RAM; 64-bit OS, x64-based processor; Runs Windows 8.1) (- I'm pretty sure it's not a lack of processing power)
Running Pro Tools 12 (standard version)
Interface: Tascam US-600 (4 Mono-Stereo audio (XLR & Instrument) inputs; 1 MIDI thru; 24 bit sample width; 84Khz sample rate) (- nothing special here)
One thing to note: I'm running the projects off of a 32-Gb SanDisk drive connected directly to my PC via a USB-3 port.