dell optiplex 745 acting very weird.?

I know its old but i want to fix it so my mom can use it. First of all i had ot working fine but it only had 1gb ram installed it cried when i used any others. Now i got 2 more ram that are the same kind as the one it had and it accepted them. But now it keeps going to recovery menus start windows normally or start syatem repair when you select normally it start loading windows then restarts and goes back to the same screen with the 2 options. When I try system recovery it loads then gives the blue screen of death. I even tried booting another hdd and it does same thing with start normal or recovery. The computer worked fine withthe one ram in it i could use the computer as well no issues. Im guessing if i take the ram out it might work but its designed to run 4 ram sticks why it only works with one?