Hi Adeel,
I would be no help about taking the PMP exam online with Windows 7. However, I can point you to Pearson VUE system requirements (
home.pearsonvue.com/pmi/onvue
), where it is clearly stated that "Windows 7 is strictly prohibited for exam delivery", so I would not take the risk.
Did you also installed the OnVUE application successfully? My expectation would be that this application would not run properly if at all compatible on that OS.
I highly recommend you to check with Pearson VUE directly, by contacting them via chat or e-mail, so they can better guide you through the process.
Good luck on your exam!
Gabriella