Do you get an error message when booting? Something like 'CMOS defaults loaded press Del to enter CMOS or F1 to continue'? If so it is probably the CMOS battery that is flat. Most computers use a CR3032 battery or equivalent. Polish the new battery with a soft cloth before fitting and avoid touching it with your fingers.
If it is a jumper problem the jumper you are looking for is the 'clear CMOS'. There will be three pins in a row with a jumper covering two. Move the jumper to cover the exposed pin and the centre pin. The only time I have known this is with brand new motherboards.