Is there some way to edit and send SMS from a desktop PC through
Windows Phone, via USB?
No. You cannot access the SMS in Windows Phone via a USB connection.
However the latest insider preview helps you to manage SMS from PC via Internet. This is achieved through the Skype app. Keep in mind that it is still in preview.
In a Windows 10 PC, You can use ...
There is an app available for Windows 7 by Microsoft which should solve most of your described problems.
Windows Phone App for Desktop: http://www.windowsphone.com/en-in/how-to/wp8/windows-phone-app-for-desktop
Since Windows 10 Mobile you don't need a PC to enable the Developer mode.
Go to Update & security
Then For developers
Pick Sideload apps or Developer mode depending on your needs.
Enabling device portal allows you to install apps on the phone via a web browser on the PC.
Windows 7 PCs can’t run the W10M (UWP) app locally (only on a ...
The drivers should just self install - it may be that they've become corrupted on your PC. One thing you can do, whilst the phone is connected, is to go into (from memory, as I don't have a Windows 7 PC to hand) Control Panel -> Device Manager - If you have any with a yellow warning triangle, right click and choose "Uninstall" - if you don't have any with a ...
Just imagine if someone steals your phone. They'd have access to everything even if they did know your code! That's not good and therefor you're unable to access the data on a locked phone.
On your next phone, enable backup to OneDrive before you do anything else!