Is there anyone that managed to install W2K8 R2 on a PowerEdge R740?
I can put in the installation disk and start the installation, but as soon I'm entering the setup I don't have any input (mouse/keyboard front usb 2.0 and iDrac)
It's not officially supported by Dell but I'd like to install it, in worst case scenario with a hypervisor
Hypervisor will be your best bet. Several pieces of newer hardware are not even compatible with Windows 7/2008R2, so there may not be a fix for it.