I did do the backup which seemed to succeed but was of such a small size that it clearly didn't contain everything important on that drive. So i started copying folders off of C and onto E. (I have three hard drives, each 1 TB.) I did that off and on for thursday and friday evening. Of course i did not shut the computer down because i was worried, given that the problem was the C drive, that once i shut it down i might never be able to get it back up again.
I finished copying all the regular data over friday night and started looking into how to do a full system backup. It turned out i couldn't do that because the backup size would be larger than the space available on the E drive. It basically wanted to back up everything on C. So first i deleted all the data folders i'd just copied over. Then i went through Steam uninstalling a lot of the larger games that i haven't played a lot of.
Early saturday morning i finally finished clearing out enough stuff that the system backup would supposedly fit on the 290 GB i had free on E. So i started the backup, and after awhile the computer blue-screened and shut down.
I tried starting it up again. It displayed a hard drive error. I tried rebooting. It booted up and got to what ought to have been the login screen but instead displayed a black screen with a mouse on it. After sitting there for quite awhile it crashed. I rebooted. This time it gave me a message about not having been shut down properly and gave me the option to start in Safe Mode. (Note to self, i need to find the key combo to force a Safe Mode start.) It actually booted up!
The first thing i noticed was that the E drive had about 10 GB left. Did the system backup finish before the crash? Or did it reserve the space first but crash before it finished the copy? I thought maybe if i started the Backup and Restore dialog maybe it would tell me if the backup was valid or not. Unfortunately either Backup and Restore is not a valid option in Safe Mode or that portion of the hard drive has been toasted, because although i could find the option in the start menu nothing happened when i tried to run it. So i tried rebooting again hoping that maybe now that it had successfully started in safe mode a more regular mode would work. No such luck.
I got busy with weekend activities at that point, but i'm thinking of trying to start in Safe Mode again so i can try individually copying game save files out of the relevant spots in Program Folders.
And now i need to figure out how to go about repairs. About a month ago i started thinking about the possibility of getting a new computer. This was spurred by my computer "coincidentally" detecting some bad disk sectors and needing to go through a disk check. At the time i decided i would wait until next year when Windows 10 comes out and see if it really fixes enough of the issues with Windows 8 to be worth upgrading from 10. Now however i have to reconsider.
Other options include getting a single replacement drive, either a Seagate (which is the kind that is failing out from under me right now, though after 4 years of use) or a Western Digital (which cost almost twice as much.) Or get two large drives which i can use to back up all the data i currently have (due to the concern that since i got three identical drives the other two might be about to start going downhill as well.) Or perform a "minor" upgrade and get a solid state drive for the boot drive and one or two other drives for storage. Or the aforementioned whole new computer.
So i went onto PCs for Everyones (the site where i got the computer from 4 years ago) and looked at the options and did some initial pricing, for both parts and a _very_ basic outlining of a new computer. (PCs for Everyone gives you a lot of options on a lot of initial configurations, final pricing on that could go up or down.)
The Best Option
If going with new hard drives, what should it be?
What Shall We Do With a Catnipped Kitty?
Or to put it shortly, i could spent $70 at a bare minimum and hope to limp along another year, $200-360 if i want to make sure i can back up everything i have right now, $500 to back up all the data and switch to solid state for the boot drive, or ~$2000 for an all new computer.
If anyone is curious, these are the two possible configurations i've come up with for a potential new computer so far: