Problem with hard drive partition

I have a problem with my hard drive partition. I have Lenovo Z460 laptop containing Windows 7 ultimate,and it has hard disk of the size 500gb. At the moment, I have 2 primary partitions and 2 logical ones but still my hard disk has 104gb free space which can be utilized by creating a new partition. But when I try to do it I got the error saying "CANNOT CREATE A NEW PARTITION. THE DISK ALREADY CONTAIN MAXIMUM NUMBER OF PARTITIONS".
I am looking for your nice suggestions to resolve this issue. Please help me out in resolving the issue.
Thank you so much!
