Peculiar backlight problem, help

Hello

I have Asus p535 Recently I have changed my PDA motherboard due to some problems. While doing That Asus gave me a free upgrade to WM6

Now after 2 months I have a peculiar probleem

My backlight does not turn up when I press the active button. Sometiomes it just flickers . Most of the time it does not turn up and I cannot use the phone

However the backlight turns on when I get an incoming call. Like wise when I do hard reset or soft rset it turns un until the windows mobile logo and goes off as soon as the Today screen turns up.

Sometimes like a mind of its own. The backlight will turn turn up normally and I can use my phone. Nowadays I have disabled turning backlight off and use the HOLD buttom to turn it off so once it turns on it remains on. However the problem still remains

To summarize in few lines

1>Backlight turns on when hard reset and reamijs till WINDOWS MOBILE logo appears and dims and turns off as soon as today screen is loaded

2>The backlight wont tuirn on with any input . Sometimes it just flickrs on and off

3<When i receive incoming call the backlight turns on and works normally

4>sometimes the backlight after flickering may turn on and the phone works perfectely for 3-4 days

I want yo ask few questions

1>Is this a hardware problem as i suppose it isnt coz phone works fine with incoming calls

2>If its a software problem is it BIOS related

3>If its software related do I need to reinstall WM6 and upgrade/ downgrade BIOS

4>Is this battery realted. however my battery does not drain fast inspite of it being 1300mah

5>My warranty is expired so any thing which can solve my problem with self help is appreciated

DETAILS

Model: Asus p535

rom date : 2007/8/9
rom version: v4.7.12 WWE_AU00
boot version: 070416122657
battery version 1.3
MP version: V0.164
Radio version :v.4.8.0
OS WM6

Any help appreciated