Downgrading Pavilion 500-037cb from Win 8.1 to Win 7

Question

I've been perusing the forum for a while now, and I couldn't find an example of my particular problem.  Whether that is because I cannot search a forum or because this particular issue hasn't come up before I can't say...but I digress.
Short version: I think I need Windows 7 drivers for a computer that came with Windows 8 installed.  I'm having trouble getting my mouse and keyboard to play nicely during the Windows 7 install process, but there may be a deeper issue at hand.
Long version (and thank you for reading this far, at least): I would like to "downgrade" my Windows 8.1-equipped computer.  I say "downgrade" but I would actually like to dual-boot both Windows 7and Windows 8.1 if possible.  I thought I knew what I was doing, but I've hit a wall (one which is likely very easy to surmount, but for whatever reason has got me stuck).
My HP Pavilion 500-037cb has been a decent cpu thus far, and I even am getting used to Windows 8.  However, there is a certain program--autocad 2012--that has compatibility issues with anything past Windows 7, and I must be able to run it for my employer.  I was told that there would be no problem downgrading the 500 to Win7, but I'm learning now that this computer was never set up to run Windows 7.  I've tried going through hp's site to find a quick fix, but I've thus far come up empty. 
First, I partitioned my drive in anticipation of the dual-boot setup.  I ordered a legit copy of Windows 7 and I followed youtube and other internet how-to's in order to alter the UEFA/BIOS in order to boot from the DVD drive.  When it came time to go through Window 7's install wizard, I could not get the keyboard or the mouse to interact with the cpu at all.  No clicking, no wiggling, no ctl-alt-del-ing, no ctl-shift-esc-ing, no nothing.  After restarting and reattempting twice, I presume that the issue is that my drivers are not set up to communicate with the impending Win7 install.  (To be honest, I don't know why this would be, as new computers are installed without internet-borne drivers every day, but I wonder if this Windows8-based computer has some sort of allergy to the HP hardware when installing Win7.) 
I've read some advice given (such as from Mr. Paul Tikkanen at http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&dlc=en&docname=c03736054&lc=en&jumpid=reg_r1002_us... and other places) but I saw CPUs that were either notebooks or otherwise unlike my 500-037cb.  Would other 500-series advice help me?  Could I use the advice of laptop questions in lieu of actual 500-037cb advice?
Furthermore, am I able to dual boot Win 8.1--> 8.1+7, or must I wipe the computer and install fresh as in 7-->7+8?  Is there any reason why the drivers would actually be the problem?  I'm able to handle a word document pretty well, but traipsing around the BIOS was hard enough, now this UEFI or whatever is cooking my goose.
Thank you for putting up with this odyssey of a forum question.  Hopefully someone can guide me back to Ithaca, if you'll excuse the pandering. 

Answer 1

Hello Mr. Tikkanen.  Thank you very much for your response.
I remember reading something about the difficulties of USB 3.0 vs. 2.0, but it didn't occur to me to switch my mouse and keyboard plug-in.
Unfortunately, my employer decided to buy a new Windows 7-capbable cpu this morning instead of having me install Win7 on the current cpu.  I was going to implement your suggestion today, but my copy of 7 was already shipped back by the time I got in today.
I actually kind of want to try it anyway for the sport of it.  I promise that, if it comes to it and I'm asked to install it later, I will attempt your suggestion and update this forum with my results.
Thank you, Mr. Tikkannen, and thanks to all you experts that search through the forums and help us get along.  It is very much appreciated.