Dell Laptop Battery not detected

My laptop says no battery is detected?
i have a dell and today my laptop just shut down by it self. i plugged in the charger but again it shut down few minutes later. i turned it on once more and i saw by the battery life thing a red x on it. i clicked on it and it says no battery is detected.please help to fix this
Answer:"I suggest that you shut the system down, remove the battery and disconnect the laptop ac adapter, press and hold the power button for 20 to 30 seconds. Now connect only the ac adapter and wait for 30 seconds and turn on the system. This will drain any residual charge in the capacitors.
Please check if the original dell Ac adapter and battery works fine on another computer. Also check if the dell pa-21 charger and battery is detected in the BIOS. To go to BIOS, restart the system and at Dell logo tap the F2 key every two seconds. Under the option General navigate to Battery information and highlight it. To the right side the battery and Ac adapter information will be listed. Check the status of Ac adapter and battery and reply with the findings.
I recommend you to flash BIOS from the link given below:
http://dell.to/1ario9m
Note: While flashing BIOS connect the dell LA45NM121 adapter and make sure the battery has minimum 15% charge as this needs uninterrupted power supply. Do not use the system till it restarts and comes up to the desktop.
Let me know the status after the BIOS update. Also check if the system turns on only with the battery and without the battery."