Re: unable to connect my lumia 730 to pc
Here's some things to check.
One - ensure your USB cable is working properly. Since it's new it should be fine.
Two - connect your phone unlocked to the PC
Since you haven't mentioned what OS you're using, keep in mind the Xp isn't supported any more and it may be difficult to find drivers for the phone if you are using Xp.
If you had an older WP, go into Programs in Control Panel and delete anything to do with Nokia. Go into Control Panel->Hardware and Sound then Device Manager to remove the old drivers for WP under Portable Devices.
Restart your computer, make sure you have an internet connection, connect your phone with it unlocked to your PC and wait for the drivers to finish setting up. It takes some time.
Let me know how you get on.