RE = Recovery Environment which is where Startup Repair etc. is located.
I'm not really sure what to advise as the machine is in the middle of what in effect is a repair install which is where your personal stuff remains intact while the OS is repaired, but something has gone drastically wrong.
Booting up with your install disk would only give you the same option of the Advanced boot options, navigating to the RE or a Custom install - but if your install disk doesn't include SP1 then you may get an error when trying to navigate to the RE.
What did the revertpendingactions cmd report and did the Startup repair run ?
If you can boot up with the install disk you would press enter when Windows Setup (EMS Enabled) is highlighted and then use the dropdown to confirm or change the language and currency then navigate to the RE.
The restore point option isn't likely to work as there isn't anything to restore from and if you had created an external system image, you would have already tried that option.
That only leaves fixing the MBR but I'm not confident this will work either.
Follow the steps for Win 7 by clicking on 5 in the side index in this article for that.
https://neosmart.net/wiki/fix-mbr/#Fix_the_MBR_in_Windows_7I don't know if that Easy Recovery Essentials is a freebie or what it does, but as you have an install disk, that may be sufficient.