if u cant get t the OS then u probaly better taken it to a repair shop. I presume u know the password have you tried to enter the password b4 it shuts down? If u cant then you probaly better taking it to a shop. IS the Password a BIOS paswword or is it the windows password. A windows password can be resolved. Another option is to try a resinstall of the Operatins System to see if that clears it up.
If you know how to try to take the CMOS battery out but that means getting very techie and it may mean taking to the shop to have it done. Is that battery charged up properly, can you try it on the mains it also be that the could an internal problem maybe with the motherboard or something else.