Windows 7 And Bios Can't Find Drives, Even While PC Running

So my system (updated specs in my profile) has been running perfectly since first built in January.Saturday, a Steam update came out. Ever since then, I have had major problems. It starts with the entire system totally freezing and occasionally BSOD.If I reset (hardware reset button), then bios can't find any of my hard drives (two different SATA channels), but it can usually find the DVD (also SATA). Sometimes it will hang on the drive part of boot up. (ACHI mode is enabled.)If I do a cold boot (hardware off, wait 15 seconds, then on), then it boots and runs fine. for about an hour, maybe two... then the above happens again. It doesn't matter what I'm doing, games, surfing, or not even at my computer. I did notice that the drives were running much slower than normal, so I updated the Intel Response Time thing (whatever you call it). That greatly improved drive response and boot time. But it did not cure the crashes.Other than verifying all the case wires were firmly connected, I haven't had time to do anything else.I can't imagine how a software update (Steam) could frack up my bios or my mb, but that is the only thing that has changed between running perfectly to totally unstable.

I'm planning to uninstall steam and reinstall.I'm not confident that will help if the update has caused another problem.I don't know if it's Windows 7, Steam, hardware, or a bios issue.