Battery Icon Missing

I have a Compaq nx6310 laptop with Windows XP as the OS. The battery meter no longer shows up in the task bar. Instead I have a icon which shows "On Ac Power" always regardless of whether I am plugged in to the power source or not.

Also under Power Schemes I longer find the options for the battery.

I have tried most of the solutions posted on the net i.e. excluding the powercnfg from DEP, disabling the SSDP service and UNPP service.

Not sure what else is to be tried.