|So, you are changing the motherboard in a Dell? |
All mATX boards use the same mounting hole pattern. The size of the board may vary slightly.
The part of the motherboard that sticks out the back of the case may not be the same. You should have gotten a replacement that matches the new board.
Why are you changing the motherboard anyway?
You need to post the brand and model of the new motherboard. Depending on what you bought, you may not have some or most of the same connection ports on the new motherboard.
Also post some details about this change. Are you changing processors and memory?
What about graphics?