PC won't post after plugging in HDD even after unplugging it again.

So, I got a new computer up and running. Windows ready to go and everything. I added a hard drive from the old computer as just another drive, not windows or anything. Pretty easy stuff. But now computer won't post.

All I've done was plug it in, it just won't post... I unplugged it and still no post. I've never seen this before...