I have a PowerEdge 840 recently de-commissioned at my shop, so I can maybe comment a bit on it hardware-wise.
Yes, the fans do spin up very loud. Most servers do anyways, but this one can be a screamer during POST.
Check to make sure you have a DVD drive - looks like this server by default actually comes with a CD-ROM only drive. That tripped me up too when trying to boot a DVD (you just don't expect a system to not be able to read a DVD nowadays, lol).
I've previously had Windows Server 2003 and Ubuntu 12.04 on this machine, so I can't comment on whether it will take Windows 7 specifically. Theoretically it should work as long as drivers are compatible. I would see your biggest hurdle being the acquisition of the RAID controller driver (assuming you have a RAID card on yours too, I'm not sure if mine came with it or if it was installed afterwards, I got this machine second-hand). If it doesn't get the RAID driver, you won't see a hard drive during install, and will have to manually either slipstream one, or hope setup will see it on a flash drive once you've grabbed it from the manufacturer's website.
Edited by Demonslay335, 15 January 2016 - 12:35 PM.