Toshiba Laptop Not Starting Up Properly

okay so I haven't had to post in support for a long time. Haven't had a computer problem in so long it was jarring when my sister came to me and told me her computer wasn't working right. The Computer is a Toshiba Sattelite C855D-S5320
Operating System
Windows 10

Processor
AMD E2-1800 dual-core APU (1.7 GHz)

Chipset
AMD A68M Chipset

Graphics Card
AMD Radeon HD 7340

Storage
500 GB Serial ATA HDD

System Memory
4 GB DDR3 1333 MHz

She said that she got a "Critical Update" yesterday morning no problems indicated and then later when she wanted to shut down the computer she got the message to either update and shutdown or update and restart. She chose to update and shutdown. Next time she started the computer up it stopped at a black screen and went no further. so she did a hard restart by holding the power button and starting it up again. This time she was told she could restore it to a time when the computer worked. She did so, but the computer then said the "critical update" did not download properly, she was told to restart and try again. She did but was greeted with a screen saying she could reset her computer without losing her files, so She did that. Finally she got to her desktop. she then got the message to update&shutdown or update&restart when she shut down her computer. now it will only go so far as a black screen again. I don't. know what is wrong let alone how to fix it. any ideas?

 

It sounds like you are going to need to get into Windows Safe Mode and explore the recovery options.
But before doing that you need to drain the Laptop of all energy:
Turn the system off completely. Unplug the power cord adapter and make sure there are no USB devices connected, and no DVDs or CDs in the CD/DVD drawer.
Now, following the user guide, remove the Laptop's Battery.
Now press the power button for at least 20 seconds to drain any remaining power.

Now reconnect it via the power cord/adapter and check whether any lights show that power is on, that is before you press the power button to launch/boot it.

Here is the product specification for that laptop model number:
http://support.toshiba.com/support/staticContentDetail?contentId=3493943&isFromTOCLink=false
Here is the user guide for the Toshiba Series of that model:
http://support.toshiba.com/support/staticContentDetail?contentId=3477465&isFromTOCLink=false

According to that, when purchased originally it was Windows 8, so I will assume that your sister upgraded to to Win 10 when that was offered free.

Here is how to get into Windows Safe Mode > Recovery in Windows 10
https://support.microsoft.com/en-gb/help/12376/windows-10-start-your-pc-in-safe-mode

I don't know the full recovery options for that Brand/Model BUT if it offers a Factory Restore, from a recovery image on the hard drive itself, that is likely to take it back to Windows 8 which is not a good idea.
If need be, a clean reinstall of Windows 10 via a Windows Installation Media download from Microsoft Download Centre saved on to a blank USB pen drive with at least 6 gigabytes of space would be needed.