i have a problem can anyone help me please

i just buy a new pc Dell Inspiron 7720 i7

Technical specifications Dell Inspiron 7720 (17R SE 7720)

Display: 17.3" (1920x1080) FullHD LED
Processor: Quad Intel Core i7-3630QM (2.4 GHz)
RAM: 6 GB
Memory type: DDR3-1600
Hard Drive: 1 TB
Graphics: Discreet, NVIDIA GeForce GT 650M, 2GB of dedicated video memory
Intel HD Graphics 4000

Network: Wi-Fi 802.11 b/g/n; Bluetooth; Fast Ethernet
Optical Drive: DVD+/-RW
Additional features: Webcam, integrated microphone, SRS Premium Sound, backlit keyboard
Connectors and input-output ports: 4 x USB 3.0 (one supporting PowerShare) / VGA / HDMI / LAN (RJ-45) / Mic-in / Headphone / card reader 8-in-1
Operating system: Windows 7
Battery: Lithium-Ion, 6-cell
Dimensions (W x D x H): 417 x 276 x 32 mm
Weight: 3.28 kg
Contents: notebook Dell Inspiron N7720, battery, power adapter, documentation
Warranty: 12 months
Color: Black


can anyone tell me how to improve video quality becoz i get a very bad picture compere to my old desktop compaq p4
note : i have instel all the drivers and every think works right except this problem ; wen i watch 480p and above the picture is great but wen i watch xvid or HDTV.x264-LOL the quality is bad can anyone help me please