I am editing mostly 2k video footage in the vse (edited down to about 40 seconds or so). I have set 25% proxies and set the scene preview to 25%. This allowed me to preview at 24fps (the fps of the footage). However I added a new strip (that for some reason I can't get a properties window for - will be a separate question). Then I couldn't preview at 24 fps, so I removed the 4k video and none of the strips previews at higher than maybe 10 fps. I have tried deleting the proxies and rebuilding, with no change. Restarting didn't help either.
FYI this is on a PC in Windows with 2 X5650 processors (XEON 2.66ghz 6 core hyperthreading) and 24 gig ram and a 2T hdd.
What did I do and how can I fix it? 2fps makes editing pretty impossible.