Just Cause 2

your gpu barely meets the minimum systemr requirements

have you turned down all the graphcis?
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Minimum:

OS: Microsoft Windows Vista (Windows XP is unsupported)
Processor: Dual-core CPU with SSE3 (Athlon 64 X2 4200 / Pentium D 3GHz)
Memory: 2GB System Memory
Hard Drive: 10GB of free drive space
Graphics: DX10 compatible graphics card with 256 MB of memory (Nvidia GeForce 8800 series/ ATI Radeon HD 2600 Pro)
Sound: 100% DirectX 10 compatible sound card
DirectX®: Microsoft DirectX 10

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Recommended:

OS: Microsoft Windows Vista SP1 or Windows 7
Processor: Intel Core® 2 Duo 2.6 GHz or AMD Phenom X3 2.4GHz or equivalen
Memory: 3GB system Memory
Hard Drive:
Graphics: DX10 compatible graphics card with 512 MB of memory (Nvidia GeForce GTS 250 series/ ATI Radeon HD 5750 series)
Sound: 100% DirectX 10 compatible Dolby Digital 5.1 sound card
DirectX®: Microsoft DirectX 10.1

pretty much yeah

Could be overheating issues or a PSU going bad. I would first monitor the temps of your CPU and GPU in the background while playing JC2 and see where they go after 30 minutes or so.

temps seem to be within normal range, and the PSU is about a year old.
I'd hope it isn't failing now. Its also over-rated for my system... so it wouldn't be too stressed

get a new GPU man..a gts 250 green is great..its safe too..low chances of overheating..

if i get a new one,
i want something a little more future proof...

gtx 460...

you should consider getting a new PSU..preferrably an 800W...with corsair,enermax,cougar or any brands that are known to ensure the your graphic cards are safe from getting barbqd...you should get GTX 400 series cards or Ati 5000 series if you want something future proof....

i have an 800W Watts BFG ES Series Power Supply