Compaq laptop won’t boot properly

Bought a used Compaq laptop and put in new RAM. Worked fine for one day. Then I took the battery out because it was too weak, thinking I can just use the AC adaptor. When I power up, the screen is fuzzy, Compaq logo came up and then the utility page. Tried the setup, default, but all I got is a screen with little bits of color.
Is this related to the battery being taken out or is it more serious?