So after upgrading my pc's cpu, gpu, and heatsink, Now i want to upgrade the motherboard, Can I use the dell optiplex 755 or 745 sff motherboard to switch with mine? will there be any chassis problems?
Well the Case for the Dell Optiplex 755 is a Mid ATX case so you can only fit a Micro TAX or Mid ATX motherboard into it. A Full ATX board won't fit. As long as it's one of those sizes than you won't have any problems. The screws will match up.
Gotta love Dell's BTX case, they really screw ya with that. In this case they are not interchangeable, a BTX motherboard will not fit in an ATX case and vice versa. I highly suggest you buy a new ATX case for your computer, one with style and a window in the side to show off your new equipment.