8310, upgraded to Singapore Telecom Mobile Pte Ltd v4.2.2.338 / 4.2.2.184 (Chinese).

I upgraded the os couple days ago, it worked fine until today. don't know what happened, the backlight doesn't turn off automatically when my bb is not in use.

here is the symptom (bb not in use, not in charge, not connect to computer):
1. no matter the screen is locked or unlocked, the backlight on for about 5 minutes, then automatically turns off for about 5 second and then it turns on again for 5 minutes... repeat for ever.
2. even I hold the mute key to let the bb goes to standby mode, backlight goes off for a few second and then turns on again... return to situation 1...
3. backlight goes off when bb is inserted in the holster. normal.

does anyone know what happened on my bb? There is no BBLight installed. Already pulled out battery twice...

If I can't fix it, how do I re-installed the same os again? I don't want to wipe it out.

Help please. Thanks!

Have you tried a hard reset? (Battery pull while the device is on). Have you recently installed any new themes?

already pulled out twice...(you replied before I edited my post).
theme were all enabled when I loaded OS, actually I deleted some of theme this morning, now I only have vodafone and bbdimention. not sure when the problem started though.

btw, my service is with AT&T(cingular).

thanks.