Originally Posted by bored_stupid
CMW does not work with ARHD. You need TWRP 22.214.171.124
fastboot flash recovery openrecovery-twrp-126.96.36.199-m7.img
Enter recovery and flash ARHD again
Sent from my HTC One using XDA Premium 4 mobile app
Thanks bored_stupid! This solved the installation problem.
The other problems were solved like this:
The first problem was that fastboot didn't connect to my PC.
This was solved by changing computer to one with a USB 2.0.
Now the problem I had with my recovery was solved by flashing the recovery partition again and clean the cache (forget that the first time).
fastboot flash recovery clockworkrec.img
fastboot erase cache
After this I was able to get in recovery mode.