I had exact same problem, was working fine and with no reason, i reflash FW = L9(safe mode)>normal boot; burn DVD>T9(safe mode) > back to normal. I trace down how this happen (maybe only in my case) : Qscan(Smart scan) on TYG02,
write DVD on 16x, after this all hell broken, reboot don't
help. I reproduce this "way to hell" 2-times.
Bottom line for me never ever run Qscan special SmartScan.
Try reflash and good luck