Random shutdown following HD 7750 upgrade

[MockTurtle]

Hi, first post here, hoping for some quick advice.

I recently installed a 7750 as a (theoretically quieter, cooler, less power hungry?) replacement for the faulty HD 4870 on my ageing machine (specs below). Now experiencing shutdowns about 5 mins after startup.

It's stable in safe mode. The latest drivers are installed; cleared the old ones with Catalyst, then checked with Driver Sweeper. I think the PSU should be fine. There's no sign of overheating - I checked with Speedfan in core or GPU.

Any suggestions regarding what else might be the problem or how to diagnose? I'm new to this, so please bear with me

Thanks

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Card and Drivers

VTX Radeon HD7750 1GB DDR3
aticfx64.dll,aticfx64.dll,aticfx64.dll,aticfx32,aticfx32,aticfx32,atiumd64.dll,atidxx64.dll,atidxx64.dll,atiumdag,atidxx32,atidxx32,atiumdva,atiumd6a.cap,atitmm64.dll
Driver Version 12.104.0.0
Driver c:\windows\system32\drivers\atikmpag.sys (8.14.1.6304, 567.50 KB (581,120 bytes), 29/03/2013 01:09)

System

Microsoft Windows 7 Home Premium
Version 6.1.7601 Service Pack 1 Build 7601

Motherboard: Gigabyte EX58-UD3R
PSU: Epsilon 80PLUS 600

Processor: Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz, 2664 Mhz, 4 Core(s), 8 Logical Processor(s)

BIOS Version/Date Award: Software International, Inc. FB, 04/05/2009
SMBIOS Version 2.4

6GB Corsair DDR3, 1TB HD

Cooling: Cooler Master V8, 3 fans (in win, not sure of exact models). However, checked temperatures using speedfan - they don't exceed 65C.

 

[humbug]

Motherboard: Gigabyte EX58-UD3R

BIOS Version/Date Award: Software International, Inc. FB, 04/05/2009
SMBIOS Version 2.4

BIOS update?

 

[MockTurtle]

Thanks, hadn't considered that. Will try.

 

[MockTurtle]

Worked, much appreciated!