Monitor black borders unused on-screen

Config:


1 x ASUS PCE-N31 Wireless Network Adapter 802.11B/G/N Up to 300MBPS PCI-EXPRESS
1 x Microsoft Windows 7 Home Premium Edition 64BIT DVD OEM
1 x Western Digital Caviar Black 1TB SATA3 6GB/S 7200RPM 64MB Cache 3.5IN Dual Proc Hard Drive OEM
1 x AMD Phenom II X6 1055T Thuban 6 Core Processor 2.8GHZ Socket AM3 Retail Box
1 x MSI 790X-G45 ATX AM3 790X DDR3 CrossFire 2XPCI-E16 2XPCI-E 2XPCI SATA2 RAID GBLAN Audio Motherboard
1 x LG GH24LS50 24X Super Multi Lightscribe SATA DVD Writer OEM Black
1 x G.SKILL F3-10666CL9D-4GBRL Ripjaws PC3-10666 4GB 2X2GB DDR3-1333 CL9-9-9-24 Core i5 Memory Kit
1 x Radeon HD 5850 725MHZ 1GB GDDR5 4.0GHZ PCI-E 2XDVI HDMI Display Port
This video card is available only as part of a pre-built NCIX PC system.
1 x NZXT Tempest EVO EATX
1 x Seasonic SS-600ET 600W EPS12V 24PIN ATX Power Supply PFC 80PLUS Bronze 6PIN 8PIN PCI-E 120MM Fan OEM


There are black borders around my screen 24'' DELL full hd in a 1908-1020 resolution.. this is not normal im supposed to be full screen..

Thanks for your help  
(And another problem is that in the device manager it says I have 2 monitors? lol ))