Ati radeon hd 4800 series crashing my system while playing skyrim

Thought it might be overheating but i downloaded SPeedFan and everything appears to be in hardware limitations...

here are my specs i grabbed from a CoH helper..

DxDiag gathered at January 23, 2012 18:19 (-05:00)
Operating System: Windows Vista™ Home Premium (6.0, Build 6002) Service Pack 2 (6002.vistasp2_gdr.110617-0336)
System Manufacturer: Dell Inc
System Model: XPS 630i
BIOS: Phoenix - AwardBIOS v6.00PG
Central Processor: Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz (4 CPUs), ~2.4GHz
Memory: 8188MB
.Net Memory Report: 6058MB out of 8188MB available
Page File: 13604MB (2983MB currently in use)
C Drive: (NVIDIA STRIPE 931.52G) 791063MB out of 951767MB (83%) free
D Drive: (NVIDIA STRIPE 931.52G) 1024MB out of 2047MB (50%) free
E Drive: (PBDS CDRWDVD DH-48C2S SCSI CdRom Device) zero-size drive
F Drive: (HL-DT-ST DVD+-RW GH30N SCSI CdRom Device) zero-size drive
Windows directory location: C:\Windows
DirectX: DirectX 11
DirectX Diag version: 7.00.6002.18107 (64-bit version)

Display Notes: No problems found.
Sound Notes: No problems found.

No problems found.

No problems found.

No problems found.

No problems found.
Input Notes: No problems found.

Monitor: LG L227W (Digital)
Monitor's Max Resolution: (blank)
Video Device Name: ATI Radeon HD 4800 Series
Manufacturer / Chip: Advanced Micro Devices, Inc. / ATI display adapter (0x9442)
Video Memory: 743 MB
Driver Version: 8.17.0010.1094
Driver Date: 9/8/2011 12:32:58 PM
Driver Language: English

Sound Device Description: Speakers (Realtek High Definition Audio)
Driver File: RTKVHD64.sys
Driver Version: [color=yellow]6.00.0001.5667[/color]
Driver Date: [color=yellow]8/18/2008 3:05:28 AM[/color]

Sound Device Description: Realtek HDMI Output (Realtek High Definition Audio)
Driver File: RTKVHD64.sys
Driver Version: [color=yellow]6.00.0001.5667[/color]
Driver Date: [color=yellow]8/18/2008 3:05:28 AM[/color]

Sound Device Description: Realtek Digital Output (Realtek High Definition Audio)
Driver File: RTKVHD64.sys
Driver Version: [color=yellow]6.00.0001.5667[/color]
Driver Date: [color=yellow]8/18/2008 3:05:28 AM[/color]

Sound Device Description: Digital Output Device (HDMI) (2- High Definition Audio Device)
Driver File: HdAudio.sys
Driver Version: [color=yellow]6.00.6002.18005[/color]
Driver Date: [color=yellow]4/11/2009 12:39:51 AM[/color]

Sound Device Description: Digital Output Device (HDMI) (High Definition Audio Device)
Driver File: HdAudio.sys
Driver Version: [color=yellow]6.00.6002.18005[/color]
Driver Date: [color=yellow]4/11/2009 12:39:51 AM[/color]


WMI Information
Motherboard Manufacturer: Dell Inc
Motherboard Model: (empty)
Motherboard Product: 0PP150
Motherboard Version: A00
BIOS Manufacturer: Dell Inc.
BIOS Name: Phoenix - AwardBIOS v6.00PG
BIOS Version: DELL - 42302e31
BIOS Release: 20080715000000.000000+000

Did this card come with the system initially? If it didn't, chances are that your crappy Dell power supply gets overloaded when the card is gaming. My recommendation would be to get a new 550W-750W power-supply.

and i just checked i got a max output 750W PS.

Go to the AMD Overdrive and reduce GPU clock settings and memory clock settings (try to find the optimal max). By default AMD seems to standard 'over-clock' their cards. Performance will still be ok, but it will not longer causing crash (at least in my case).