After my SSD failed, the only other option was to revert to a standard hard drive. Since then, I've noticed that the system cannot endure more than 12 hours before experiencing intermittent lockups which can elapse between 1 - 5 minutes. It doesn't outright crash or shutdown, it just simply locks up for a short period of time. While it probably doesn't help having 80% of system RAM in use, I'm still curious of what causes this issue and of what can be done to remedy the system of it. Oh, and I'm using Windows 7 x64 as a primary OS (a clean install).
There are a couple of possibilities:
Since you mention waits of 1-5 minutes, I'd check the event log for indications of hard disk timeouts. If you replaced the dead SSD with a new one, then this might mean the motherboard I/O controller is dying. If you replaced the dead SSD with an old disk then this might mean the old disk is dying, but for my money I'd guess motherboard.