Some drives aren't detected anymore

I've been having some issues with my hdd as of late.

So on my main PC i have 2 x 320GB Seagates (O/S) in a RAID0, a 500GB Seagate (random files) and a 1.5TB Seagate (storage).

I was on my HTPC last week and was streaming some movie from my 1.5tb hdd. All of the sudden, the movie stopped. Went to my main PC and noticed my 1.5tb wasnt scene by windows anymore, device manager and manage computer option didn't see it anymore as well. Restarted PC, saw it in bios. Everything was back to normal.

Yesterday morning, I get on my computer (leave it on 24/7) computer was acting really weird. Sluggish and crtl alt delete wasnt working, so I did a normal restart(let windows turn off the PC). Then upon start up, I got missing boot file error. Popped Windows 7 CD in and did a system repair and it fixed the boot file. Thinking it had something to do with the RAID0?

I remote access my PC from work alot and I was torrenting this DTS Demo sampler and than I got some weird error from utorrent saying can't download or something. I looked around and noticed my 500GB wasn't detected anymore just like how my 500GB was.

None of this has happened before up until I setup my RAID0 last week or so. I ran HDTUNE on all the drives and they are in good health with 0 errors. When I did my RAID0, I reinstalled windows 7 x64 and haven't overclocked it yet.

Any ideas, thanks.