Disk Check Dual boot

Disk Check Dual boot

I am trying to dual boot ubuntu with windows 8 on a new laptop. I have
sorted out the flash-drive with the iso, set up with the Universal usb
installer.
I have then set the laptop to boot from flash.
When i fire the laptop up I get a grub menu asking me whether I want to
try ubuntu, install or check disk.
If I try ubuntu or try to install it gets stuck (installing gets stuck at
the screen with ubuntu and the alternating white & orange dots underneath,
selecting the try now brings up what looks like a ubuntu desktop but then
freezes).
If I select check disk it tells me that one error is found, which is that
it can't find:
pool/main/g/grub2-signed/grub-efi-amd64-signed_1.9~ubuntu12.04.3+1.99-21ubuntu3.9_amd.deb.
Having checked the flash drive it seems that this file is indeed there,
where it should be.
Any suggestions are greatly appreciated....
Thanks!