Hi.

When I turned on my PC I saw after 30 minutes that something was downloading. I opened update/recovery and it was the new build 10074 that was downloading. Okay. Now after 45 minutes about 3 GB were downloaded but nothing is happening. No windows with the restart options and in the update/recovery windows it still shows that 25% are downloaded.

What should I do? Restart?

I don't think you have download about 3GB already. you were only able to download 25% of build 10074. you might have problem with internet traffic. you can restart and retry to download the build or wait for it to finish.

I have an Internet monitor and I did not use other apps.. The monitor and also my provider data are showing that I have downloaded 3.01 GB

I did a restart. Now it shows this:

Nothing is happening

You may have had other prerequisite Security updates that installed during that reboot.  You could try another reboot if it has not yet begun the install, or your OS Build settings may be set not to install automatically.  That would be under the Advanced Options shown at the bottom of the Windows Update image you posted.

I tried about 15 reboots. And as you can see there is another issue with the advanced options. I can't select how to get builds, fast or slow.

This Build 10074 is on both Fast and Slow on the same day.  Once you get it installed, it may resolve some of these issues.  Can you either maximize or stretch the size of your Advanced options dialogue box longer or scroll down to see more?

You could try changing your setting at the top from automatic to Notify to Schedule Restart, then exit and re-launch Windows Update and/or yet another reboot to see if you get prompted for the install.

My Advanced options from Build 10074 looks like this:

If all else fails you can download the new Build 10074 ISO and upgrade from within Windows by mounting it and running Setup.exe.

Download Windows 10 Insider Preview ISO April Update