I can't Edit powerpoint file on browser

Hi everybody

I almost fail to open powerpoint document in browser each time i try to do so

I kept looking and searching aroumd for hours for a solution and found nothing that help

The big problem happen when I try to edit power point document on browser I get the following problems

1- The CPU kiks to 100% and so the RAM (using hyper-V with machine that have 4 cores and 5 GB of RAM)

2- The browser display error (An error occured)

3- After some tweaking got different error "powerpoint can't open this presentation for editing because it's locked by another user"

The solutions I followed

1- Checked all services are running

2- Start web client service on win7

3- change the application pool associated with the Powerpoint service to "SharePoint Web Services Default" and changed the managed service account associated with it, through sharepoint Central Administration

What should I do?