after reading all the received mails that slim tower inspiron 545s can have a graphis card

I went to buy one for my computer at the dell service center he told me that the graphic card requires a good cooling facility which my computer didnt had

he did not recommend me to buy a graphic card

he told me that mine pc was not good for games

Can you help

I want a graphic card for playing games like gta 4 and spider man 3. I want shader version 3.0 or higher.