It sounds like you are having a partition problem, if you imagine a hard drive as a whole pie, partitions would be slices of that. In order to have two operating systems on your machine, when you installed Ubuntu; partitions we're created; these partitions represent their own "drive" so this may be the reason that you only see 50 GB of your 500 GB hard drive in Ubuntu. As for windows, you will have to use 3rd party software to view your Ubuntu partitions in it; they do not run off the same type of file system!
Windows pretty much runs on file systems know as NFTS and FAT32, while Ubuntu runs on a file system known as ext4; so mounting a ext4 drive in Windows is a daunting task; its better to let a program do it than to mingle on it in your own. Imagine NFTS and ext4 as french and tagalog; they just do not speak to each other.