Won't Boot. Black Screen With Blinking Cursor Upper Left

Computer is Compaq desktop running Win 8.1. It had just updated and I'd turned it off and was turning it back on. It was booting very very slowly and I had to leave. I didn't want to leave it on, so I turned it off by pushing and holding the on/off button for 5 seconds. Now it won't boot. I went into CMOS and ran a hard drive check. All good. I tried the restore function but after "Windows is loading files" the screen just goes black and nothing happens. My fault, I know. But what can I do? Fortunately all my data is on a portable hard drive, and I have this laptop for a backup.
Keith

 

Some cases just letting it go for a while it will right itself. A while has been overnight is some cases...

 

The first thing I would do is to disconnect the power supply/cord and then press the power button a couple of times...
Then reconnect the power cord and turn on the pc as normal.
Not sure why it works but it's part 1 in my 'belt and braces' rescue procedure.
Good luck.
s.

 

Try shutting down, disconnect power supply completely
Then press and hold down the start button for about 15 to 20 seconds.
Then , re-connect .
Start up ,and wait to see if any change -with luck it could start O.K, but give it a coupe of minutes, if it does not.
If it did not start properly, do not hard shut down- Instead press control , alt, and delete buttons to see if it will restart - this has sometimes worked for an interrupted update, and has then rolled back the update, and got a computer working
Sorry to appear to post similar to Stephen- He posted whilst I was typing-

 

Thanks. Working on it.

 

Well, I had to do a system restore. This time it worked. Unfortunately the computer reverted back to its original operating system, Windows Vista, and in the process, back to its default factory configuration--which does not include wifi. I have an A6100 WiFi USB Mini Adapter that the satellite ISP installed, and I have the installation CD. The computer opens the autostart file just fine and runs through the process until it gets to plugging in the adapter. I plug it in and the computer can't see it. I tried it on all four of the USB ports with the same result. I know the USB ports are good, at least at a basic level, as I use a wireless keyboard and a wireless mouse and they work on all of the USB ports. So now I think I have a software problem. Can an administrator move this to a software forum for me?

 

Might be a long shot, but have a look at system restore , and see if there are any more restore points - there may be an outside chance of the time it ws originally upgraded to Windows 8.1.
If no luck there, - Have you the coa for W 8.1? -Have you a W8.1 setup disc/usb ? If not you can download an iso and update to 8.1f rom here
https://www.majorgeeks.com/files/details/microsoft_windows_iso_download_tool.html
Just choose your version of W8.1.
Just hope you have the COA......