Running Games in Dell XPS 1645

[@vi]

Hi all, recently (just two days back) i purchased Dell XPS 1645 laptop & the configuration as follows,
core i7-72QM
4gb Ram
ATI raedon 4670 - 1gb

today i installed Batman Arkham Asylum Demo. when i started the game, it was running smoothly for few mins, some 10, after that it started lagging & the speaker was producing noises (krrrrr....) along with game music. I minimized the game, when i started clicking on my computer or right clicking on desktop, it was too slow. it took a minute to open task manager. later i ended the game using task manager. earlier it was at native resolution, i.e. 1920x1080. i reduced the resolution to 1280x1024, & still there was same issue.

so guys what's wrong with my laptop ? what you suggest solution for this ?

thanks in advance.