@monton I know next to nothing about Apple products so be gentle with me. Is it not "booting" (loading the OS), or not POST -ing. (Power On Self Testing).
OK, a Windows machine "POSTs", then presents a BIOS roll. The most important part of the "POST" is a memory check. The BIOS then registers all the system components, and loads the OS.
So where exactly is your machine stopping?
The last machine I had which cleared POST and BIOS, then refused to load the OS, turned out to be a bad video card. I thought I ruined the board in an additional memory install, almost gave up, yanked the card, and lo and behold, Windows loaded immediately after I hooked up the monitor to the CPU's IGP ("IGP" = On board graphics built into the CPU).
A bad C:/ drive would cause this as well. So might malware, but as we all know, (or have been led to believe), that doesn't happen to Macs.