GB overload ...large files

This is a two-part question .....

Out of 2 years using GB I have gotten the old "Part of the Song Did Not Play" warning many times - but in the last day it is on every song practically- even with songs that previously weren't an issue - even when I lock the tracks.

I was recording and using many live instrument tracks, using effects and it was fine - all of sudden GB hit molasses and won't play today.

Do I have larger system issues?

- Hard Disk has been close to full for a while (2 - 8 gb space)
- Battery just went kaput days ago
- been deleting cache files, etc - hope I didn't mess anything up

Also:

one song / file is 6gb huge! while most others are under 1 mb or in the 10s of mb?
why is this one 6gb - it's not the only one with lots of tracks and effects

any help is appreciated

andy