BootMGR disaster

I started my PC this morning and was greeted with a BootMGR missing error, i followed a few things online including going into the CMD and entering the following codes;
bootrec /RebuildBcd
bootrec /FixMbr
bootrec /FixBoot

They didn't work so i've decided it would be easier to just reset my OS, however if i try to reset i'm told i haven't enough space in my C drive. So how can i make space without being able to go into my PC properly?

Tl;dr my computers bricked and i would really appreciate some help, cheers

How much data do you have on the computer that you need to save?

You are going to need a couple of USB thumb drives or DVDs. Assuming you have access to an operating computer, install Macrium Reflect Free and make a Macrium Reflect Free rescue disk (USB flash drive or DVD/CD).
Macrium Reflect Free


Then download a Windows 10 ISO file:
Windows 10 ISO Download - Windows 10 Forums
and make a USB flash drive (or DVD):
USB Flash Drive - Create to Install Windows 10 - Windows 10 Forums

I highly recommend just using option 1 of the second tutorial above to both download Windows 10 ISO and make the USB or DVD as it does it all for you.

Boot you problem computer from the Macrium Reflect Free Rescue disc. Under the restore menu is a utility to fix startup/boot problems, you can try that first. If that doesn't work then you can make an image of your existing Windows and save it to an external hard drive or possibly network location. You can later install Macrium Reflect Free and browse that image to retrieve your data.

If Macrium Reflect Free fixes the boot problem, you are good to go. If it didn't, then you will have to boot from the Windows 10 install USB/DVD that you created and do a clean install of Windows 10.