Let us know what model of Dell it is.
A lot of Dells use proprietry motherboards that only fit in a Dell cases. Most of the time though, the rest of the hardware (RAM, CPU, drives etc) is standard & will fit non-Dell boards.
As a replacement mobo from Dell will probably be expensive, you might be better off buying a different motherboard & case, then transferring everything into that.
Can't say for sure though without knowing what the exact model number is.