Hi there,
Thanks for your question. Tuesdays are automatic Patch-Tuesdays when security patches and fixes get pushed out from Microsoft to everyone that's running a W10 computer. Sometimes, about once a month or so those updates (Windows Updates) will cause your computer to reboot. If your computer has any issues, or the version of W10 is out of date, settings will get changed inadvertently due to changes in the computer's Registry from the Updates. Usually, the settings can be manually changed back to what they were prior to the changes caused by WU. However, in some cases it requires more advanced software repairs up to and including Windows reset or Windows reinstallation.
It would be helpful to know
WHICH version of W10 your sis-in-law has, W10 Home or W10 Pro. In the last few months we recently found out there is a flaw in W10 Home which does
NOT allow you to turn off these automatic updates, nor can you reschedule them for a convenient time such as in the middle of the night when the computer is not being used.
W10 Pro (which costs twice as much) does have those 2 capabilities and thus you can disable Windows updates so that they do not interrupt her while she is running a program. Most people today tend to run multiple programs concurrently, and when one or more of those programs is writing to your hard drive and a forced Windows update comes in and reboots your computer, this can cause damage to the data files on the hard drive, or in some cases as we've seen, crash the hard drive where it becomes in-useable and the data on it can even become unrecoverable unless you send it out to Professional Data Recovery which can cost many hundreds of dollars.
The other thing we've noticed, is that many W10 computers are bought used or even Refurbished, and they have the 2 older versions of W10 which pre-date the W10 Anniversary Update from last Aug. 1st 2016. Since you didn't tell us
WHEN she purchased the computer or the build date, we are left to guess that. Older Pre-AU Windows10 versions such as v10240 and v1511 can become mucked up if the update coming into your W10 computer is the v1607 (Post-AU update). This newest update almost always causes W10 to crash and or malfunction, and should not be attempted. A Clean Install is the recommended method to convert your W10 version to post-AU. To check your sis-in-law's computer for her W10 version, do this: use the keyboard on her computer and use
<windows+logo-key and the R-key> simultaneously. This will bring up the Windows Run box. Type in the command
"WINVER" into the Run box, and hit the
<enter> key on her keyboard. This will bring up a small screen with the exact version of her W10. Please post that back here so we can identify which version she has. I'll post a pic of this for you below. This process only takes 5-minutes, and will help us to identify which version her Dell computer is running and then make specific recommendations to you for repair. There are about a dozen sub-versions of W10 v1607 now, and the latest is
v1607 b14393.693.
Here's a pic of the WINVER command information screen:
Another thing we'll need to know, is whether or not your sis-in-law has W10 Home or W10 Pro as I asked above; so we need 2 pieces of critical information to help you. Post both of those answers back to this thread. To find out which version of W10 she has, right-click on the White Windows Logo Start Flag on the lower left corner of her W10 desktop, on the large menu that comes up, select SYSTEM option and left-click it. This will bring up the System screen, and at the top, under
WINDOWS EDITION you will see either Windows 10 Pro or Windows 10 Home. Sometimes, it will just say Windows 10 without the word Home on it. This is indeed W10 Home, and unless you see the word
"PRO" in that description, it's still W10 Home.
Here's a pic of the SYSTEM screen:
Gathering these 2 pieces of information may take you 10 min. or so and another 10 min. to post back the answers.
In the mean time, you should try to simply manually reset her login from Password back Pin options and see if that works. 3 minutes. Go to
OPEN ACTION CENTER->ALL SETTINGS->ACCOUNTS->SIGN-IN OPTIONS. Select PIN, and re-enter her 4 digit PIN and save. Exit and reboot her computer. That should fix it for her!
If it doesn't, after you post back your SIL's (sis-in-law) information we asked you for we can make more recommendations on further troubleshooting you should do to identify the problem and repair or reinstall W10 as mentioned.
Since you've been on W10 for 7 years, I'm hoping this won't be too difficult for you.
Best of luck,
<<<<BIGBEARJEDI>>>>
Many people create a Pin and don't write it down, and when it fails 6 times, W10 will revert to making your enter the Password that was setup when she originally turned the computer on for the first time after taking it out of it's factory box. If she forgot that Password, she has to go through the normal W10 Password Recovery which is posted here on WF; just use the Search box to find it.
If they have to Reset W10 or completely reinstall W10 it will definitely cost you more. Computer stores are having to deal with this now more frequently since W10 Home can't disable the weekly updates, and lots more folks purchase computers with W10 Home than W10 Pro, due to the often lower price point, so they are getting their computers scrambled more often. 
