Audio / video problems on 17 5755

I've had no audio from the PC's internal speaker for almost a YEAR! In settings>sound, the volume bar is at 0, and an X there that I cannot move, nor make the X go away, period. Says below that no audio devices are installed, but sound properties says that Realtek audio device is working properly.

I've allowed THREE different Microsoft Level 2 Techs use their "Log-Me-In Rescue" Tool without success. The last one says that he KNOWS what the problem is, but since only Dell supposedly can fix it, the only thing he can do is a clean install of Windows 10. I have vast percentage of files and folders backed up on an external hard drive that will hold 1TB, so there is PLENTY of remaining space in the BIOS. Tech savvy, I am NOT. Not even close, but I know messing in the PC's BIOS is dangerous for a large percentage of PC owners. I've taken it to a Microsoft store. THREE different Techs there concluded that they had NO IDEA what was wrong, and offered me $75 toward a trade-in on a new laptop! I mean, Yuk, Yuk, they didn't realize how absolutely STUPID that was! I paid over $700 for this Dell 17 5755 AMD quad-core (it doesn't act like one). 

Someone in the CNET forums gave me a Google /Dell /update-package link, and says that should fix the issue, but also gave me a link to THIS community, to see what can go wrong. Also, perhaps get a pointer or two on how to proceed. I neglected to mention that my Bluetooth external speaker works beautifully, and video is normal speed. BUT, with Bluetooth earbuds / headphones, audio AND video playback is in super slow motion.

I don't cotton much to the idea of a clean install, since it will wipe out everything that's left on the PC, including all of my bookmarks, passwords, etc. I watched the Microsoft Tech send a boatload of stuff to the external hard drive, but he did it so fast that I've no idea what is on it, nor do I know how to view it by hooking it back into the USB port. Told ya I'm NOT tech savvy, and I've gotten the wife to help me so much that she is so PO'd about it that I dare not ask anything more...she'll find something heavy to throw at me! 

A Firmware update in the BIOS.  THIS is the link the CNET forum person gave me. https://www.google.com/search?q=Dell+17+5755+bios+update+package  JIMINY CHRISTMAS! HELP!!