issues with video editing

i've been trying to edit a 6 min video on and off all night. it went smoothly for about the first half of the process, but the system doesn't seem to be able to keep up changes or even playback now. things are constantly freezing, endlessly buffering or going blank. This has been happening since ~6pm tonight (its now 11) and I've closed out the project, the site, my browser; I've let the project alone for more than an hour, and every time i come back to it, i end up running into the same problem within a minute or two (if it even manages to fully load the video in the first place).