Hi, I was starting to play Portal but as soon as it loaded my screen switched off. This doesn't happen while playing Microsoft flight simulator 2004. Could someone please help I really want to play Portal! 


My Computer
- Computer Manufacturer/Model Number
- Hewlett-Packard dv6
- OS
- Windows 7 Home Premium 64bit
- CPU
- AMD Athlon II M320 Caspian 42nm Tec
- Motherboard
- Hewlett-Packard 3635
- Graphics Card(s)
- ATI Mobility Radeon HD 4200 Series (HP)
- Monitor(s) Displays
- Generic PnP Monitor 1366x768@60Hz
- Hard Drives
- 298GB Western Digital WDC ATA SATA
- Mouse
- Logitech M195 Wireless and Integrated touchpad