Thank you for the tips, Don (et al).

As mentioned in the opener I already tried to install in safe mode.

Now I tried to copy the data from the disc to the drive, but I got this error:
"Cannot copy HelperDLL: Data error (cyclic redundancy check)." 

I restarted the computer, and tried again, but got the same error. 

My DVD-R drive is fine; I used it for backup this morning. I am beginning to think that I got a faulty installation disc.

Do you have a tip how I could copy the content of the disc or get a new disc (or download the content of the disc)?