No bootable device

Just wanted to check in and let you know the drive has been operating without a crash since last night. I'm not confident the issue is resolved, though. Still planning to use the CD as instructed whenever I experience the crash again. I was reading the Microcenter tech's notes regarding the Crucial SSD firmware update, which is the only 'repair' that's been performed. Seems to relate to a failure at power up. In my situation, however, the failure occurs during Windows operation even when the machine is simply idle with no applications running. I wish I knew why the drive has been functioning for almost 24 hours without crashing because there doesn't seem to have been any fix applied other than firmware update that doesn't address what's happening, and I had a crash after booting the computer at home with the update installed. The only other change is uninstalling Avast, but other computers here are using the version I had on the crashing machine, all the same settings, and have no issues from it. Thanks again for all your help. I'll check back when the random crash occurs.

I try to follow that advice, too :) The 64gb SSD that came with the machine never had a problem, and I never installed firmware updates. I was happy with it and only replaced it to have more space available. I was told Crucial is a good brand so didn't expect any problems with the 256.

That's a great price! I will look into that brand, thanks for the recommendation :)

That was an amazing price. Just checked and it has gone up but still reasonable. I'll be watching for another sale! I was happy to read that you have a positive opinion of Crucials, too, since you seem very knowledgeable. I'm learning as I go and hoping this 256 behaves!

I'm back with another update, hopefully the last :) The machine ran flawlessly for two days, I made sure everything was backed up again. Shut it down (nervously) last night and tried booting this morning. No bootable device, plus another message I hadn't gotten before: "A disk read error occurred. Press ctrl/alt/delete to restart". I did this three times, and on the 4th attempt, the message was back to C drive not recognized, "no bootable device". [I'm editing to say that the machine wouldn't recognize the macrium disk, and in trying to use the Windows disk, I couldn't do anything because the message said there was no drive to install to.]

We took the computer back to the shop and finally appear to have an answer -- the motherboard needs to be replaced. I'm cynical and still wondering if this is, indeed, the solution because we've been told two times already that the computer was fixed only to find the problem persisted. Fingers crossed this time!

Will be spending this snowy weekend reinstalling everything and hoping the computer is finally fixed!

Thanks again for your kindness and advice, whs. You're an asset to this forum and you certainly helped calm my nerves! I will post again if necessary, but for now will try to be optimistic and mark this thread as solved. :)