Where to find download link for msert.exe (Win7 home 64 bit)?

You will need a flash drive to do this

A CD will do instead of the Flash Drive.

Download ComboFix from any of the links below but rename it to svchost.exe before saving it to your Flash Driver or CD. <- Important.

Once you have it downloaded to your Flash Drive or CD, I want you to save it directly to your C:\ drive. Be sure to do this in Normal Mode.
Double click on the renamed ComboFix.exe & follow the prompts.

If you still have trouble,

There could be various reasons for which system is not able to repair.

We need to check the policies and registry settings and exceptions and firewall settings and other kind of settings.

For a quick solution seek an expert's help from the following chat link.