Display setting in BIOS

Hi Everyone, Am facing a strange problem. I have a Dell Inspiron 1000, 2.2Ghz Celeron processor, 256MB RAM, 80GB HDD. In the BIOS setting there is a setting for Display, which is set to XGA 14.1". This setting automatically changes to 'Unknown' & the screen does not display anything when you 'ON' the laptop. The boot up screen too is not displayed. However, the laptop boots fine into Windows XP ( this is observed when you connect an External monitor to the laptop's VGA port). I have also observed that if the value in the BIOS is 'XGA 14.1" ' then only the laptop recognises the display. I have
tried changing the CMOS battery , but with no results. I also tried to reset the BIOS settings to 'Factory default' settings, still of no use. If at all I managed to open the BIOS settings ( whenever the display is visible), the 'Display' setting keeps on fluctuating intermittently. Also, cannot change the values manually.
Basically, in the BIOS setting, there are two values for Display - 1) XGA 14" and 2) UNKNOWN. These values cannot be changed manually. However, they change automatically from 1) to 2) & back to 1). I want the value fixed at 1) only that is XGA 14"

Kindly help. Thanks for attention.