I have windows server 2012 datacenter with hyper-v role that I tried to upgrade to R2 RTM.

All went fine until the reboot and the error "windows cannot start the installation process"

I can start windows server 2012

I must say that I used a ISO file using DRAC for the install.

Is there a log to check for errors?

Hi,

Just a thought, check to see what your BIOS settings are on your computer.
This problem is usually related some potential problem in the disk or BIOS or faulty hardware. The BIOS sometimes limits the read/write scope of boot sectors, to avoid virus attack. 
Review the BIOS setting, if theres any Anti-Virus settings, just disable it, and then start the install again. 

Regards,

Yan Li

The machine i use is a 720xd from Dell can You refer to server bios settings that could lead to the failure?