Repair Win 10 MBR?

Hi Forum Folks,

Stepped squarely in it this time!

5755.  Out of warranty.  Came as Win10 only.  Went to set it up as a dual-boot with Linux, and got zero help from Dell Support.  Managed to do it anyway (thanks, Dell....) and it's been running just fine for over a year, til today.

Was tooling around in Win10, when it suddenly became almost completely unresponsive... took forever to load a webpage, or pull up an app.  Then I'm getting bombarded with popup windows telling me about add-on and plug-in crashes.  The hard drive light is on solid (I can hear/feel the disk spinning like mad).  Worrying about a virus or malware or what have you, I tried killing the network connection, but that was unresponsive too.  Tried to pull up the 'Start' menu... no joy there either.  Tried CTRL-ALT-DEL, but again, no response.  Getting desperate at this point, I pulled both the AC adapter AND the battery.  That stopped it alright!

Trouble is, now it won't boot into Win10 at all.  Being dual-boot, I get to the "Grub" screen, select Win10, and get nothing but a black, dead screen; no cursor, no little whirligig dots... nothing.  For a very long time.  Linux boots just fine from the same place.  Tried booting into one of the recovery discs the thing prompted me to burn when I first got it... result is the same: dead black screen

Thank the powers that be that I ignored Dell's direction that I not turn it into a dual-boot, otherwise I wouldn't be here right now.

I'm fairly certain I've managed to trash the MBR; I understand that this is a not-unheard-of result of  improper shutdowns... and they don't come much more improper than this one was.  I'm in the middle of downloading a recovery image and some sort of recovery tool from Dell; no idea how that's going to pan out.  Most of the stuff I've been able to find assumes that you can boot into Windows, at least into Safe mode, but I don't get even that far.  So most of that advice is useless in this instance.  I'd appreciate anyone's input on what course of action I ought to pursue, or from anyone who has managed to recover from a similar situation.  Thanks in advance!!