Various Crashing Issues

I work at a public library, and some of our patron computers are having a few issues. As calling the IT company costs a lot of money, it would be very beneficial if I could fix them (as a 17 year old who works part time, my pay has already been accounted for in the budget, as well as the fact that i "know" the most about computers here).

I have 3 issues I need help with, all of them are completely different.

1) This computer randomly freezes up. after a seemingly random amount of time of nobody using the computer it just freezes, requiring a "hard" restart. I have tried timing it, but I haven't found a pattern. I am not sure if it freezes when people use it, but I think it has once or twice. I am just wondering what kind of issues can cause a computer to completely freeze up.

2)This computer has an issue that has occured with other computers here, although I have never been able to fix it. it wont boot up, and a message saying that the system file in system32/config is corrupted/missing. all forms of safe mode/other boot options do not work. my plan is to copy the system file from another computer, and replace it using ubuntu. I am just wondering whether or not it will work.

3)This computer is the strangest in my opinion. when logging on to the patron (or the admin) account, it freezes while it is "loading personal settings". When I try to run the computer in safe mode, it still freezes up while logging into the patron account, but not while logging in to the admin account (although it froze up when i tried using system restore).

Once I was in safe mode, this message popped up on my taskbar.

mcuicnt.exe-corrupt file
the file or directory c:\system volume information\...restore\46de8921-1d39-44d2-a9e9-64119261f211\rp1046\change.log is corrupt and unreadable. please run the chkdsk utility.

One time while restarting this computer, I encountered a blue screen, although I don't know when it happened, as I often do something to the computer, and leave for a while before coming back. It had a really strange code though, and if I find it again, I will post it here.

Thank you if anybody can provide assistance.