Try a power reset.
Remove the battery and then press and hold the power button for 30 seconds to drain any residual power from the laptop, plug in the charger (leave the battery out at this stage) and try to start the laptop.
If it starts allow it to boot to the Windows desktop, wait until the HDD activity settles then shutdown in the normal manner, switch off the charger, replace the battery, switch on the charger and try to start the laptop.
If the power reset doesn't work try removing /replacing the laptop's RTC battery to see if this restores the BIOS to a default condition. (Just disconnect the battery's cable connector from the motherboard there is no need to actually remove the battery itself)
Here is a link to the service manual for your laptop. Scroll to Sect 4-39 to view the necessary pre-requisites and then the procedure to remove the RTC battery