I have an OCZ Vertex 2, SMART on it is reporting no errors and OCZ own diagnostic tool reports drive health as 100%. It is undoubtedly the drive though, first Windows 7 will hang mid-use and complain that system critical files such a explorer.exe are not found, etc... On reboot, about 50% of the time, the disk itself is not found by the BIOS. Is there anything else I can do, diagnostic I can run to confirm my suspicions? I'm on Windows 7 64 bit
If it's only being seen 50% of the time by the BIOS, and falling off-line in the middle of using it, then try a new cable, new power tap and/or power supply.
If those don't help, try it in another computer, if it still does it there, then you know it's the drive, if it doesn't, then it may be your motherboard/hard drive controller.