'No Signal's Screen After Booting from HDD

Hi all! This is my first post, so please forgive me if I'm posting in the wrong place.

Anyway, I've been using Ubuntu for a while by just loading it live off a flash drive, seeing as the computer had no hard drive at the time because of a bad windows install. So I found an old working hard drive and put it in. I booted up the flash drive and hit 'Install Ubuntu'. After waiting an hour or so after setup, it said the install was successfully completed, and I reboot and tell the computer to boot from the hard drive and not the flash drive. The Ubuntu logo pops up for a few seconds, then the screen goes black and the monitor says 'No Signal Detected'.
So I tried one of the fixes I found online (adding 'nomodeset' in place of 'quiet splash' by editing the option from the GRUB menu) but that didn't fix the issue, it just caused it to boot to a command line after Ubuntu's GUI failed to start. I also tried booting into the recovery/safe mode option, but the same thing happened. It worked fine off a flash drive, which is what confuses me. I even was able to load the nVidia drivers on the flash drive version and have it work fine.

Computer is an old, outdated HP Pavilion s7000-something, 1GB RAM, 400GB HDD, nVidia gfx card (can't remember which one.)