Hello Latif, Here are the drivers for the LTO4 tape drive that you have & you will need to install them to get the drive to be seen.  www.dell.com/.../powervault-lto4-120hh  Secondly with the last 2 lights flashing amber that could mean that the drive may not be at the home position.  what you can do is to hold in the eject button for about 20 seconds till the drive reboots and see if that resets it to a ready state.  With the drive having amber lights it will not be seen by the OS in most cases.   Please let us know if you have any other questions.
I wanted to find out if the PoverVault tape drive we have (SCSI) is compatible with Windows 2012 R2 server. Currently have this connected to a Dell PowerEdge R710 using Adaptec 29310LPE card. Server picks up the card ok, but I am not able to get it to see the drive itself. We have not used this drive for a long time and information I was able to see on the drive is LTO4-EH1 and P/N 45E3731. Thanks.
LTO4-EH1 PN 45E3731 Compatibility