Can I downgrade from Windows 10 to Windows 8 without losing personal apps and files?

I don't know the procedure for it, but I can help you with getting your internet connection while you're in windows 10.

Just go to device manager

Click windows button along with R ( windows + R ) or you can open by clicking RUN option.

type- devmgmt.msc and click Ok. You will be redirected to device manager.

There you can see all your drivers and devices.Now see which is the device you are using for internet and update that driver.

Update all the drivers ( which should be done after updating it to windows 10 ). Then restart your system. Hope this solves your connectivity problem and stay with windows 10 it's awesome.

Even when I upgraded my Bluetooth drivers and screen brightness drivers, Audio drivers not functioned. By following the above procedure all came just back to normal.

If the default Windows 10 recovery is failed then your only option is to format. And after format you get to rewrite the boot entries as well. As your current recovery failed from official Windows 10, your only option left is formatting the existing setup. If your system is functional (as if if you can access the desktop) then you can take backup of the existing data and then format.

You can't revert to previous OS if the Windows 10 has failed to revert the upgrade. Officially there is no way to fix the failed upgrade.

Windows 10 is the latest and final release by Microsoft corporation. I would not suggest you to revert back to any previous Windows edition because they will not receive any new updates in future even critical ones. But in case you want to do it then Windows 10 comes with in-built downgrading capabilities to revert back to previous OS but you deleted all your backups so it will not be possible as well. There is another option to install Windows 8 again with either Bootable Pendrive or DVD. Here are the steps you should follow :-
1. If you have a Windows 8 DVD then skip this step or Download PowerISO and use it to create a bootable USB device.
2. Insert your USB device and restart your PC, you will enter in boot mode same as it happens on a DVD.
3. Click on Install and accept Terms & Conditions. After that you will be prompted with two options - 'Upgrade' or 'Custom'. As you are on the latest version of Windows so you will not be able to use upgrade feature. Choose Custom and choose your installation drive. (Note: - Don't format it while installing Windows otherwise you will loose all your backups and files.)
4. After installation process completes you will be greeted with Windows 8 welcome screen. Navigate to installation drive, you will find a folder named 'Windows.old.xxxx'. Open this folder and you will see all your software, save files present there. Just copy them to your preferred location.
Apart from your Windows installation disk, no other storage disk will be affected or altered during this process.

I will not suggest you to go for any other Windows edition other than Windows 10 because it is latest and last one. It will receive regular updates and is the only Operating System with DirectX 12 support. As you are facing Internet Connection issue, you can follow steps below which will help you in solving your problem.
1. Install all updates available for your device and OS. Each and every update comes with some tweaks and improvements over previous one. (I faced display resolution issue, I installed all the updates and the 2nd last update fixed my problem.)
2. Go to Device Manager and check if their is any malfunction in your internet device. If you have sound technical knowledge then disable it and uninstall its drivers. After disabling click on 'Scan for Hardware changes'. It will re-install the drivers and enable your hardware. Most of the time it solves internet connection issue.
3. If you are using any router then check its configurations. I myself faced this issue when I installed Windows 10 my router was reverted to default setting and I have to call my ISP to solve this issue. So just check it and call your ISP and get it solved.

I will not encourage you to downgrade because it will solve your current issue but it is 100% sure that you will face problems further which can be only solved when you upgrade to newer version of Windows which is Windows 10.

Don't tackle with the problem, solve it.

Regards,
Joy Joon

If it is only the internet connection problem, then you don't need to get into all the complications to go back to the earlier version. Rather focus only on the internet connection problem.

Apparently what it feels like, you need to set up your internet connection once again by following the same installation procedure.

There you have to go to:

Settings > Network and Internet> Choose the type of connection from the given list > and follow the rest of the instructions.

If this doesn't work, call your internet service provider and fix it up.

This way, you get your stuff secured and start working with the latest version as well.