recorder suddenly slow

[xlr8]

hello
tonight i have found a problem recording a blu ray disc
using lg ggw-h20l unit on win xp sp3

until now, i was able to record blu ray media at 2x, with the buffer indicator at 100% steadily

tonight it seems i can not go above 1.3x, and the buffer indicator fluctuating between 30% and 50%

even the rewritable speed for blu ray is slowed, and dvd also are slower

i have benchmarked every component of my pc (cpu, hard disks and ram) and they are all at same level as usual, so i can not find any bottleneck

no hardware changes, no software changes, no virus and so on, every hdd defragmented, same media brand etc

this can be a faulty drive? of there can be another cause? someone could suggest me some test or some software for understanding it? it seems it works well, apart the speed of anything it does is half the normal...

the sole component i have not checked is the power supply, i do not know any program than could check it, someone knows if it is possible the unit is slower because it is receiving insufficient current or voltage?

thank you for attention