16.04 GRUB menu keys?? HP pavilion laptop

     I reboot my laptop and I see the splash screen animation, it ends, then I see the BIOS screen, which is constantly flashing from text to black. Looking at the beginning of the text, it reads the number of 'files and blocks ' and at the very end, it states ''starting Show Plymouth Boot Screen...'. *edit* : . I wait about an hour for the issue to resolve, but nothing changes.

    I've tried a few methods to get to my GRUB menu via the splash screen.

holding SHIFT + ESC
Pressing CTRL +ALT + DELETE
holding the RIGHT SHIFT
holding the LEFT SHIFT
holding 'C'

*EDIT* finally, got myself logged in, and the text reads the following:

    welcome to Ubuntu 16.04.3 LTS (GNU/Linux 4.13.0-3 generic x86_64)

   *documentation ....https://help.ubuntu.com
   *Management https://landscape.canonical.com
   * Support https://ubuntu.com/advantage
    Linux ##### 4.13.0-37 generic #42~16.04.1-Ubuntu SMP etc....

    935 packages can be updated.
    0 updates are security updates

     ~bash: /home/#####/.bash_profile: Is a directory
      #####@#####:^$

What commands should I be trying rn?

I just tried upgrading 16.04LTS to 18.04.3, and now the flashing BIOS screen won't go away, preventing me from getting to my desktop.