SSD suddenly unconfigured and not listed in boot order

I put together this PC around Christmas, and everything until now has worked fine. The main boot drive is a Crucial M4 128GB with Windows 7 64-bit installed on it. I recently came back from a week long vacation to discover some problems.

It seemed fine when I first got back. I surfed the internet for a while and played some games and then went to get dinner. When I came back, I had a black screen that said "Reboot and select proper boot device. Or insert boot media in selected boot device and press a key".

I then restarted the computer and a screen came up during the boot process that showed my SSD as unconfigured. That screen stayed there for a few seconds, and then the PC booted up fine. I didn't think anything of it until once again I got the "Reboot and select proper boot device" screen after a few more hours of working on the PC. The error screen didn't show up until I had left for a while, so it might only be appearing after idle and coming to a screen saver. I have yet to encounter the error while currently doing anything on the computer.

Just now I booted into BIOS (UEFI) to see if there was visibly anything wrong. I noticed that the SSD is no longer listed in my boot order, but my secondary storage drive was listed. It seems the SSD all of the sudden disappeared. But, it did show up in the list of drives and I could manually boot to it without any issues. I do still see the screen during booting up that says the SSD is unconfigured though.

TL;DR: SSD suddenly appearing as unconfigured and not in the boot order list in BIOS, though booting to it works fine. After idling for a few hours, the computer will crash and show an error screen saying to reboot and select a proper boot device.

Does anyone have any ideas what the issue could be?
Thanks!