hmm, seven hours later it's still frozen. But let's make a step by step guide.
1. plug to usb
2. unninstall rockbox and delete all files from the drive
3. download and copy official sansa firmware
now, how do I restart Sansa to official firm.? The ON + LEFT obviously doesn't work... will it work if I wait for the battery to die again and press left when plugging in to the usb?
IT DID WORK.
SOLUTION: Once the battery goes down, plug in the usb cable and press LEFT at the same time. It loads the OF. Then just uninstall Rockbox, copy the official firmware, flash OF, send it for repairs and install Rockbox again. Voila.