Hi Dmitry1975, What is the hard drive configuration on this system, is it non raid, an S300 controller or an H200 controller? What version is the BIOS at? Version 2.1.2 added support for installing server 2012. The best way to install the OS is to use our Systems management tools and documentation DVD that will load the drivers needed for the OS install. Burn this to DVD and boot to it. Choose the Server OS installation option and follow the prompts to start the install.
I've created a bootable DVD using Win Server 2012 ISO, I changed boot sequence in BIOS but getting "led on this computer." after which nothing happens. Any help will be highly appreciated.  Thanks. 
DELL PowerEdge T110 Cannot boot from DVD