You already named the problem : Fan runs at full speed all the time and the computer won't boot.
You could try unplugging the box, popping out the CMOS battery and waiting 1 minute until the power completely discharged. Plug the PC back in, then put the CMOS battery back in and configure the system time in the BIOS and then exit and let it reboot. If it starts it should scan for a bootable device, find the disk and boot into Windows.
There's a few people have had trouble with 100% fan speed in Lenovo PCs. A simple Google search should give you lots of relevant threads - Hang on; you DID try a Google search for yourself, before posting here. You did, didn't you?
Anon, July 2016