Grub not working now, after working for a week.

I installed Ubuntu 16.04.1 about a week ago on a partition from my Windows 10 OS. Since then, I have been able to successfully use Grub to choose either windows or Ubuntu to boot. Just now, however, I restarted and the Grub menu didn't appear. The bios menu also did not appear. It then booted straight into Ubuntu. This happened after I tried to hard restart with the power button and the prompt appeared suggesting that I save files first. My files were all saved, but I exited out and saved them all anyways, and then shut down just from the actual software option. Settings seem to have changed as well. For example, my desktop is now stuck at 1024x768, while before I was at 1920x1080. The only other option is 800x600. This was the case before I installed drivers for my graphics card. Also, when I signed into gmail, it recognized me as logging in on a new computer, even though I have logged in on this before. I've tried holding down shift on startup, and it still just boots straight to Ubuntu. I have updated Grub as well.