Problem has been solved with the help of Bestami Bayramoglu from Dell Tech Support team. I took some photos of the back panel of server and library and sent them to Bestami. They analyzed and told me that SAS cards were not inserted and locked as they should be. These cables have a locking mechanism and they do not work if they are not inserted and locked correctly. Another issue for readers; the part number of SAS cards inside my server R620 is j53x3. This card's metal slot is not compatible with my rack server. The correct one's part number is 3ddjt. Bestami told me about this and we will order the correct one. Thanks for your support.
Hello.  We have a Poweredge R620 server with Windows 2008 R2, two Dell 6gbps SAS HBA cards installed and Simpana 9.0 R2 backup software. We also have a TL4000 with two IBM drives, all firmwares are up-to-date. Each SAS HBA card is connected to each drive of the library via one SAS cable. I can see the cards in the Device manager of the server. The library is working, but when I monitor the drive status from the web interface of the ilbrary, both port A and B seem "not ready, not connected". I tried to use Simpana to detect the library. But it cannot detect anything after tens of trials and different scenarios. What am I doing wrong? I can provide any information you want. Thanks in advance. 
Dell 6gbps SAS HBA and Powervault TL4000