Can't mount the fourth partition

I had this problem too when I bought my first Apple Mac. What Dwarf said is true.

I see you don't have a genuine Mac but if you did, genuine Macs use a partitioning scheme called GUID which supports up to 128 primary partitions (but not extended partitions). However, although Windows works with the GUID partitioning scheme, it works by pretending that it's a traditional MBR scheme. The MBR scheme supports only 4 primary partitions, any one of which can be an "extended" partition.

The good news is that OS-X works perfectly well with the older MBR style partitioning scheme. So if your scheme is MBR, you should delete Ubuntu and turn all the subsequent free space into an extended partition. You should then be able to re-install Ubuntu and successfully create your shared partition. You'll need to reconfigure your boot loader too, of course. But note that this is ONLY possible with an MBR partitioning scheme. Even though it supports more partitions, you can't achieve what you're trying to achieve with the GUID scheme.

Thanks guys for all your help, Ima try what ever you guys said to make this work. I'll keep you guys posted on my results

Hello everyone once again!!!!
I almost got what I wanted to do work. Still though I cannot see my 350 GB partition in my computer but it says that it is active in my Disk Management. Here is what I did:
First Partition - 350 GB Shared Volume (Where all 3 Os's will share common media files)
Second Partition - Mac OSX
Third - Windows 7
Fourth - Ubuntu
I partitioned all these using Disk Utility in the OSX. If you need more info on what I did please ask me and I'll tell.