I have had portal 2 for a while but one day it launched went black then said portal 2 exe not working I deleted then re installed and it worked but now its saying portal 2 exe not working again heres my system info

Processor Information:
Vendor: AuthenticAMD
Speed: 2700 Mhz
6 logical processors
6 physical processors
HyperThreading: Unsupported
FCMOV: Supported
SSE2: Supported
SSE3: Supported
SSSE3: Supported
SSE4a: Supported
SSE41: Unsupported
SSE42: Unsupported

Network Information:
Network Speed:

Operating System Version:
Windows Vista (64 bit)
NTFS: Supported
Crypto Provider Codes: Supported 311 0x0 0x0 0x0

Video Card:
Driver: AMD RADEON HD 6450

DirectX Driver Name: aticfx32.dll
Driver Version: 8.892.1.1000
DirectX Driver Version: 8.17.10.1094
Driver Date: 24 Oct 2011
Desktop Color Depth: 32 bits per pixel
Monitor Refresh Rate: 60 Hz
DirectX Card: AMD RADEON HD 6450
VendorID: 0x1002
DeviceID: 0x6779
Number of Monitors: 1
Number of Logical Video Cards: 1
No SLI or Crossfire Detected
Primary Display Resolution: 1920 x 1080
Desktop Resolution: 1920 x 1080
Primary Display Size: 26.65" x 15.00" (30.55" diag)
67.7cm x 38.1cm (77.6cm diag)
Primary Bus Type Not Detected
Primary VRAM: 512 MB
Supported MSAA Modes: 2x 4x

Sound card:
Audio device: Headphones (Realtek High Defini

Memory:
RAM: 8191 Mb

Miscellaneous:
UI Language: English
Microphone: Not set
Media Type: DVD
Total Hard Disk Space Available: 1430696 Mb
Largest Free Hard Disk Block: 695503 Mb
OS Install Date: Dec 31 1969
Game Controller: Gamepad detected