Win 7 won't boot after I reverted back to it from Win 10

Gazzer mate I don't know quite what you want to do but if you have all your data saved then you could try a factory restore because if it was a factory installed 7 then there would be a factory recovery partition that when used will take the machine back to as it came out of the manufacturers site - as new . Now this will lose the data and programs of course which is why I asked if you have your data backed up.

Now what you do is to hit the restore key while booting in most cases but beign a Dell I am not sure but this may give you a few options
How to restore your Windows 7 computer to factory settings | Dell US

Let us know how you go.

Just as a by the by mate what didn't you like about 10 as I resisted for some time and there are ways of setting it up to look like 7 and personalise it to your particular tastes. Myself I have it set to just show me the Control Panel This PC (Computer) ans System Configuration plus the weather and photos at hitting Start I got rid of all those ridiculous apps like crushed candy games News and suchlike.

Yes mate better grab a 7 OEM soon as they are getting quite scarce out here and cost as much as a 10 OEM.

To be honest I have got quite to like it after setting 10 up as I like it and it is much faster.

The privacy stuff and bugs have been sorted out a bit better now which was why it took me so long to decide to use it.

If you change your mind there is is this Classic Shell - Start menu and other Windows enhancements don't use the beta but it does really make 10 look like 7 does anyway that is your choice the only thing is changing the Start button icon - can be done but a fiddle

The pic is of my main laptop with 10 set as I want it - a bit blurry as it is on a 27" monitor

Gazzer I went the clean install way mind you onto a new drive and used the generic code to activate it then on this machine I used my 7 Pro key to activate it take a look at this Clean Install Windows 10 Directly without having to Upgrade First - Windows 10 Forums

Now of course it is your budget but a small SSD would be the way to go or even a spare drive that you can clean / wipe would be the go there - so much easier than upgrading I found and a lot less grief.

Say something like this SanDisk Ultra II 2.5" 240GB SATA III Internal Solid State Drive (SSD) SDSSDHII-240G-G25 - Newegg.com-Newegg.com < good drives I like them or this Samsung 850 EVO 120GB 2.5" 120G SATA III Internal SSD 3-D 3D Vertical Solid State Drive MZ-75E120B with OEM USB 3.0 Adapter and USB Cable-Newegg.com again excellent drive and you can set them to boot and use a larger spinner for data

To be honest what I normally do is to clone the original drive and use the clone to upgrade or try something so if the trial goes belly up then you just swap the original drive back in

No probs mate it happens to all of us at some time or another. Once you have the 10 on then this is handy to use much the same as the same form of tutorial in 7
Optimize Performance of Windows 10 - Windows 10 Forums > you can lose a bit of "bling" but it does make the machine faster and more efficient:)