I couldn't have fullscreen with either of my Pc.

Does it have to do with the GPU? I think not. Because when I had Windows Xp,
I could have fullscreen resolution of 320x240 without any problems. But since I've changed to Windows 7- I can't go below 640x480. No matter what drivers I use. Even installed the same GPU driver and Dx version I had in win Xp. But no luck.

Didn't work on my Desktop [980 Ti]

Or the laptop that I'm using [Mobility Radeon Hd 3400]

Or with the notebook.

It's not a problem with monitor either. Because the same monitor could give 320x240 in win xp.

How you managed to have 320x240? Do you have Amd or Nvidia Gpu?