As said, netinstall can be very tricky to run, and sometimes it simply doesn’t work, but on a next reboot (or the next-next one) it does, do check (a couple ones, there are more):
http://forum.mikrotik.com/t/netinstall-instructions/123631/1
http://forum.mikrotik.com/t/mikrotik-basebox-keeps-beeping-rebooting/143638/2
A common trick - that sometimes helps - is to use a “dumb” switch between the PC and the Mikrotik device boot port, this - for whatever reasons - allows to etablish connection when a direct link doesn’t:
http://forum.mikrotik.com/t/netinstall-fails-to-detect-router-cannot-install-routeros/157545/1