I had a linux distro installed and made the mistake of formatting the Linux drive from Win 7. Created bootloader problem in that any attempt to boot from a USB or CDROM with bootable Linux on it goes to grub error screen with "Grub Rescue" prompt.

I can still boot into Win 7 OK via the F11 menu that list all the drives, but that method will not boot from a Linux USB stick as it normally has done in the past and it also goes to the Grub Rescue prompt.

I even changed the Bios order of boot to USB, CDROM, Win 7 but the result was for the CD that you could hear the CDROM working like it was going to boot but then up came the Boot loader error. This was the Linux CD that booted fine before today.

You will have to reinstall linux or go into bios and change boot order to make windows first in boot order. Usb boot problems either have to with how usb was created or bios settings, cd booting problems is either cd or bios settings or bios boot order.

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I think you're booting to grub on the hard drive and that is why the usb fails to boot. I however don't know if your usb ever did have grub on it so I'll have to assume this usb is correct and that you are booting to a hard drive order choice and not a usb order choice.

Have you tried running update-grub?