Had you converted to EXT4 at any point? The kernel built in to Pinnacle does not support that. If so, go into Recovery and flash whatever kernel you had loaded before.
In fact, if you have a Galaxy S screen coming on, you must have been on an i9000 ROM (otherwise it would say i897 right
). If you were on i9000, almost all of those will convert you to EXT4. You will either need to flash one of the KH3 oneclicks to re-partition everything, or I would try flashing the Samurai Kernel onto it from Recovery. Either should work.
EDIT- If you did flash an i9000 ROM, you might get better functionality by also flashing the i9000 bootloaders. I am trying out Mosaic now, and find my sleep deaths SEEM to have stopped, and battery life improved, after flashing i9000 bootloaders. If you are going back to Pinnacle or a Captivate ROM, you will want to stay on i897 bootloaders for sure.