Have you done the basics like update all drivers on the machine?
please download VLC Player and try playing the media with that once all drivers updated as with the specification of your machine you shouldn't really have too much trouble unless it's a Bluray rip you're trying to play.
Spec of your machine for others:
Processor: 2.2 GHz Intel Pentium Dual Core processor E2200
Memory: 3GB DDR2-SDRAM
HD Capacity: 320GB
Graphics Card: NVIDIA GeForce 9300 GE
Operating System: Microsoft Windows Vista Home Premium
Main Specifications
Processor
2.2 GHz Intel Pentium Dual Core processor E2200
NVIDIA nForce 630i chipset
Memory
3 GB DDR2-SDRAM
2 DIMM sockets
Storage
320 GB SATA 3G Hard Disk Drive (7200 rpm) with up to 13 GB partition for system recovery
DVD writer SATA DVD RAM and Double Layer supporting LightScribe technology
15 in 1 memory card reader
Communication
Ethernet 10/100BT integrated network interface
Wireless LAN 802.11 b/g
Video
NVIDIA GeForce 9300 GE with PureVideo HD technology (DVI/VGA port, HDMI port)
256 MB dedicated memory, up to 1535 MB total available graphics memory as allocated by Windows Vista
Sound
High Definition Audio 5.1
1 front audio port, 3 rear analog audio ports & 1 rear digital audio port
Included accessories
PS/2 keyboard and optical mouse
Ports & Expandability
1 external optical drive bay, 1 internal HDD bay, 1 Pocket Media Drive bay
1 PCI-E 16x low profile
1 PCI-Express 1x low profile (free)
6 USB 2.0 ports (2 in front)
1 FireWire-IEEE-1394 ports
Software
Microsoft Works and Microsoft Office Home and Student 2007
60-Day Trial Version
Roxio Backup MyPC
Microsoft Internet Explorer 7.0
Windows Mail
Adobe Reader 8.0
HP Total Care Advisor
Photosmart Essential
Windows Photo Gallery
Windows Media Player
Windows Movie Maker
Windows DVD Maker
Cyberlink DVDSuite Deluxe
Muvee AutoProducer
EasyBits Magic Desktop
HP Games Console with hours of free game play, featuring EA Spore Creature Creator
Windows Media Center
Warranty: 1 Year Manufacturer Warranty