I replaced a motherboard and found that the new one is 24 pin.
Would this cause my video and a few other components not to work?
Should I change the power supply to a newer one?
Okay it the 4 extra pins are for a ATX standard called EPS12v which is a new form of atx12 for 'multicore' systems where four additional pins are included, an 8 pin connection is introduced for processors, and 2 additional molex are added..
So if you have a multicore processor, it would be wise to get a 24 pin power supply as the 4 extra cables (or pins) are used to give slightly more power to the system. If your using a single core system (as I suspect since the original motherboard came with a 20 pin connection, just plug it in and it'll be fine.)