Turn off Plymouth to see kernel boot messages

When your computer boots up normally there is a purple screen with cycling dots. Kernel messages are hidden from you. If you computer stops to “think” for an hour we need to know what step is causing the delay. To see the steps do the following:

sudo -H gedit /etc/default/grub

This opens up gedit text editor find the line that starts with:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash ..."

Change the line to read:

GRUB_CMDLINE_LINUX_DEFAULT="noplymouth ..."

Save the file and exit `gedit. Now run:

sudo update-grub

From now on when you boot up you won’t see a fancy splash screen but rather scrolling kernel messages. The message(s) it pauses a long time at you can write down or take a picture of with your smartphone. Then post these messages into your question.

Reverse the above steps to get your plymouth splash screen back, ie use “quiet splash…” in place of “noplymouth…”. Note the ... represents other instructions you may or may not have. DO NOT enter ... into the command.

Windows 7 turn off Hibernation

OP is using Hibernation in Windows 7. This article: Disable Windows hibernation and free up disk space provides steps to turn it off:

1. Click Start, and then type cmd in the Start Search box.
2. In the search results list, right-click Command Prompt, and then click Run as Administrator.
3. If you are prompted by User Account Control, click Continue.
4. At the Command Prompt, type powercfg.exe /hibernate off, and then press ENTER.
5. Type exit and then press ENTER to close the Command Prompt window.

See the link for more explanations and helpful images.

Windows 8/10 turn off Fast Startup

For other users, it could be a case of Windows 8/10 “Fast Startup” causing Ubuntu to “Slow Startup”. Please read this article: How to disable Windows 10 fast startup (and why you’d want to) highlights:

Why disable fast startup?

Leaving fast startup enabled shouldn’t harm anything on your PC — it’s
a feature built into Windows — but there are a few reasons why you
might want to nevertheless disable it.

One of the major reasons is if you’re using Wake-on-LAN, which does
not work when your PC is shut down with fast startup enabled. Others
would like to save the hard drive space that is usually taken up with
the hibernation file, and Linux users will likely see complications
with dual boot and virtualization. Furthermore, some users have even
reported that power buttons on their keyboard will not work and fans
in their PCs will continue spinning. These problems are by no means
across the board, but they can prove to be frustrating.

Steps to disable Fast Startup

1. Right-click the Start button.

2. Click Search.

3. Type Control Panel and hit **Enter** on your keyboard.

4. Click Power Options.

5. Click Choose what the power buttons do.

6. Click Change settings that are currently unavailable.

7. Click Turn on fast startup (recommended) so that the checkmark disappears.

8. Click Save changes.

Visit the link above for these same steps along with images and narrative.