graphics card help?

I got a new desktop to play games but everygame i play is laggy and choppy. Ive tried bit trip runner, portal 2, and minecraft and all of them are choppy on the lowest settings. My desktop is a AMD Athlon II x4 645 quad-core processor with 4gb DDR3 memory. What I dont understand is I had a previous laptop that was only duel core processor and it ran alright with all three games but its worse on my desktop! :(

Does anyone know what im doing wrong?

Return it and go to Computer Hardware for a proper build.

Sounds like it has integrated graphics.

Cuz your PC sucks.

Return it.

Well i was hoping i didnt have to because it will cost about 35 bucks to return. I think it just needs a better video or graphics card but idk :/

does anyone know where i can get a pretty good gaming pc for about... $300 or alittle more? or am i being too cheap?