I feel your pain.
If you upgraded to Windows 10 more than 30 days ago you won't be able to simply roll back to your previous 7 or 8.
I'm in a similar position as I upgraded from 8.1 months ago when 10 first launched it's free upgrade. I have had the Start Button & no modern apps working problem several times but one or other of the fixes sorted it until I installed the 112015 major Windows
10 update, since then I have been stuffed & hobbling along with a broken system as I cannot afford to lose all of my old software, programs & settings by a full re-install, (like you I don't have discs for some of the stuff).
To access the System Restore options with a broken Start Menu;
- Hover your mouse over the Start Button and RIGHT Click on it - select Control Panel and Click, this should bring up the old style Control Panel
2) Click on the Recovery icon - you should then see the system restore options to see if there's a restore point available (Open System Restore).
If there is a restore point there then you can try restoring to it to see if that solves the problem, (Windows 10 deals with Restore & Recovery differently than previous versions of Windows but you can still create manual restore points the same as always).
I assume that there won't be any restore points there, (all of mine were wiped by upgrading to the latest 112015 build of Windows 10), so you can also try accessing the modern recovery system like this;
- Hover your mouse over the Start Button and RIGHT Click on it - select File Expoloer and Clikc
- On the menu bar you should see the modern settings symbol with the words Open Settings below - double click on that, (may seem a bit slow to appear but should open the modern settings box).
- Click on the Update & Security icon
- Click on the Recovery option
- Select the Go Back To AN Earlier Build option - see if it will allow you to roll back your system?
If not then you are back to square one.
Good luck.