Optiplex 755 Stalls At Screensaver After Win 10 Reset

I finished a Windows 10 Restore/Reset my Optiplex 755 desktop, 62 bit Windows Vista business edition that I upgraded to windows 10 last year. After reset three days ago the boot stalls at the Windows Date and Time screen. Not very urgent as I have a laptop but do need to determine if I need to replace my home office desktop or if it is worth it to fix this one.

Have tried the following:
Tried: Going into Safe mode five times. Result: Will not go into repair mode or beyond splash screensaver after windows 10 screen icon spins.
Tried : Everything in Bios, order of reboot, power management, everything including reset. Result: No improvement.
Tried: Rebooting with update of Bios and drivers with CD. Result: Nada
Tried: Rebooting with Windows Repair image: Result: Nada
Tried: Unplugging motherboard and checking interior connections. Result: No change
Tried: Unplugging peripherals. Result: Nothing
Other issues:
Bios now says no hard drive present, had a floppy diskette fails error that I fixed by shutting off that mode in Bios, only two drives now available , cd and usb and Sata Drive.

Any help or advice will be , of course, appreciated.
Alexandra

 

No hard drive present in bios suggests connection problem, if hard drive has not failed.
Check hard drive connection- if a spare hard drive is available, try substitution just to see if it shows in the bios

 

Connections seem fine, diagnostic tests all pass. I have no extra hard drive but I did notice when I opened the casing of the tower, a connection that had no match to connect to. There are three wires with tines, two of them plug into the hard drive the other is just dangling. Could be the problem?

 

Can you take a picture and upload it- it would help to see the connection- Is the sata lead plugged into motherboard, or, adaptor secure ?