If you got it from someone else they may have removed the button battery inadvertently.  you need to have the cr2032 coin battery installed for proper function of bios such as remembering the changes you make and save (unless you keep it plugged to wall constantly).  you may be able to run the pc without the battery with bios at default settings.
The service manual on the Dell website for incorrect, even though it's the manual that corresponds to the service tag. The motherboard in the manual bears no resemblance to the one in my PC (e.g. wireless card shown in the manual but not on my mother board). Is there a 'proper' database matching manuals to say the Express Service Code or some other way to access the correct Service Manual?
Inspiron 3268 Service Manual