Tried installing Mint 17.1 64bit, deleted Windows 8.1 boot partition when I overwrited it with the Linux boot

As the title says, when live-usb installing linux mint 17.1 64bit, I chose the windows 8.1 bootup partition as the bootup for linux, so when the boot menu appears and I try to run windows 8.1, it re-runs the linux menu infinitely...

So I went on the live-usb again and deleted all the stuff i used to install linux on my hard drive, and now as you might think, my computer has no way to start working.

I also have windows 7 installed alongside windows 8.1, so I was trying to get a triple boot running, and screwed up. What would be the best way to get the bootup for windows 8.1 and 7 running fine again, and just scrap linux for the time being?