Hi Folks,
RE: Problem with backlight turns off after 5 seconds on Nokia 5800.
I upgraded my firmware to ver 5, and still the sam problem, i.e. light goes out afte 5 seconds..
To fix this problem on my phone I Hard Reset My phone.
1.Backup all you phone contents First, as it Will be Erased.
2.Turn phone off
3.Press and hold GREEN + RED + CAMERA buttons then Power ON your phone
Keep all keys pressed until you get the shaking hands. That should fully reset the device.
Hopefully this will fix your screen going dark/lights-out problem after 5 seconds.
Regards,
Derek.
P.S. If it doesn't work for you, then upgrade to the latest FirmWare available to you and try it again.