Well, take out the usb for starters. Next is make sure you have the trusted boot file added to your bios in your computer. I bet this is your first uefi laptop. I keep telling people to post a bug on ubuntu for not telling people they need to do this on the install.
I searched and it seems to say you need to change to cms mode in advanced options.
You could also try boot-repair.
When all else fails, change to legacy boot and reinstall.
You need to make a usb with live linux creator or universal usb installer for legacy. This is broken until 16.04 gets active again with a new startup disk creator.
I have had both methods work in my acer laptop and settled on legacy.
After the bios update, it was forgetting my trusted boot files that I was setting. I dropped back down to the older bios and then went legacy for both win 10 and lubuntu.
Do not get confused between two problems. Usb legacy boot problem and uefi. You need to activate uefi to find the secure boot settings to add the trusted source. You also need to set a password to see that option. Be very careful when setting a bios password. Be sure to reset it back to nothing by setting password again and hitting《enter》.. (nothing). If you forget the bios password, you have big problems so set it back to nothing once you are fished adding the trusted source.
Again. I recommend legacy. So..
Make a proper new usb installer.
Switch to legacy boot.
Install.
Finished.
I needed to change the partition to mbr in order to install windows as legacy. Not a big problem unless your are over 2 to (I think). You are limited to 4 paritions too. (Almost a problem for me)..but I only have 32gb anyway.
