the fact that the partition is still around and you can see it in Windows doesn't mean that it has a valid file system. Maybe the filesystem got corrupted. The real test is whether or not you can mount the partition in another Linux system. Can you boot at all?
You said it had been running for a month, that rules out the most frequent cause: people build a new kernel and don't compile ext2/ext3 support in, or have no IDE disk drivers. You didn't rebuild the kernel, did you?
You can try to boot the RedHat CD in rescue mode, or, if you can still burn a CD somehow/somewhere, I have a rescue CD project at
(there are links to some others, which are also good), either way you can boot from the CD and check out the partition.