another question can a PSU cause your GPU being bottleneck coz of insufficient power? i mean like will it the gpu getting slower or something?
Nope. For two reasons: One, the GPU uses maximum power when you turn the computer on; the computer wouldn't turn on if there was insufficient power. And two, you have a very old and integrated GPU, which won't really take any power at all.
Which I also believe is where the lag is coming from. Your GPU is about 5 years old and it was one of the weakest at the time anyway - try turning off Windows Aero (just use Windows Basic theme).