Motherboard problems galore

Question

I have 3 different Gigabyte motherboards each seems to be messed up in a different way. The GA-7VT600 that will power up but won't stay on for more than 15 seconds. It has been known to have ram problems. I have a Gigabyte 7NF-RZ which refuses to turn on evan after I've checked all the connections. I also have a Gigabyte 7VM400M-RZ that has a AGP slot that does not work. If anyone has any ideas that can help that would be wonderfull.