Some things to check off the top of my head:
1. When it is in this state, check to make sure that
Preview mode didn't get accidentally enabled.
2. What do you have your system set to under Tools > Options > Audio > Output Format?
If you're using WASAPI "vanilla", try WASAPI Event Style instead (or vice versa). The "five second" playback could be an audio driver borking up and so all you get is the initial buffer. Generally, the way this should be configured is as follows:
1. If you have a well behaved, manufacturer provided ASIO Driver, use ASIO mode.
2. If not, and you are on Windows Vista or newer, use WASAPI Event Style.
3. If you have trouble with WASAPI Event Style (no playback at all or stuttering and crashing), try switching to WASAPI "vanilla".
4. If you have a more esoteric DAC, you might have to tweak settings under Options > Audio > Output Mode options. This should be pretty rare for normal hardware.
5. If WASAPI doesn't work, for whatever reason, then either fall back to DirectShow (and get better hardware/software) or if you are on Windows XP you can investigate Kernel Streaming.
Lastly, if you've done other customizations (especially more esoteric things like RAM playback and whatnot) try turning those off to see if you can isolate what is causing the issue. Put the DSP back to stock (you can make a Library Backup to save your settings before you make changes), to see if something in there is causing it.
And, lastly, check:
1. For updated sound device drivers (this may be your graphics card drivers if you're using HDMI output).
2. Check that Anti-Virus isn't interfering. The easiest way to do this is usually to just uninstall the AV Software completely. Even with "MC" excluded, I've seen AV software still interfere in a variety of esoteric ways. If you remove it, reboot, and can still recreate the problem, then we know for sure it isn't anything to do with the AV software on your system (and you can put it back and move onto other potential causes).