no, that motherboard will not work with your existing tower.
GA-MA785GM-US2H is a good baord i just used it in a build for a freind,he ran into the same issue coming from a dell.
your dell is a BTX formfacor board, adn that is a micro ATX motherboard sowhile you may be able to make it work somhow it will not just screw right up
your PSU is also nonstandard so you would not be able to just buy a standard psu for your case, aparently the screw pattern is a dell prioritary so you're stuck with getting and PSU upgrade from dell
good news is you can get a fairly cheap small form factor case that would work for your build with that board and may even come with a better powersupply or you can get one without a PSU and get a good one (which is what i'd reccomend doing)