Corsair 4GB - Need some help

[Coinoperated]

Hello, I've just recently bought Corsair 4GB DDR2 XMS2 PC2-6400C5 TwinX (2x2GB) from Overclockers but i'm having some trouble getting it to work. Each time I install it and power up all I recieve is a 5 second beeping sound, which occurs every other second and wont let me get anywhere. I Put back in my old memory which is High Performance 800MHz DDR2 SDRAM - 2GB - 2 x 1024MB" and it works fine, so i'm a bit confused.

I admit i'm not that good with hardware, so I bought the RAM assuming it would be fine, both being DDR2. Does anyone know what i'm doing wrong? I've got Vista 64 bit with windows service pack 1 and the latest updates. If the RAM is not compatible with my setup, could you please direct me to a 4GB type of RAM which I could use instead.

My setup is:
Manufacturer: Alienware
Processor: Intel® Core™ 2 Duo E4500 2.2GHz 2MB Cache 800MHz FSB
Memory: High Performance 800MHz DDR2 SDRAM - 2GB - 2 x 1024MB
Hard Drive: 250 GB Serial ATA 3 Gbit/s, 7,200 RPM with 16MB Cache
Video Card: HIS ATI Radeon HD 4850 IceQ 4 Turbo 512MB
Monitor: 19" Dell UltraSharp 1907FP Black Flat Panel LCD Monitor
Operating System: Genuine Windows® Vista Home Premium 64 Bit

This is the RAM I bought.
http://www.overclockers.co.uk/showproduct.php?prodid=MY-136-CS&groupid=701&catid=8&subcat=813

If anyone can help me out i'd really appreciate it.

 

[nathanc]

Are you leaving old the RAM in?

The motherboard probably only supports 4GB... you will have to leave the old stuff out.

 

[RJC]

What motherboard have you got, also sometimes a CMOS reset works.

 

[Coinoperated]

I wasn't using the old RAM with the new.

Motherboard: Alienware® Approved NVIDIA nForce 680i SLI Motherboard

 

[hohum]

Is your new RAM rated for a higher voltage than the old sticks? If so, then try setting the higher voltage in the BIOS whilst the old sticks are installed, shut down, then change them over.

 

[Coinoperated]

K it turns out that one stick is faulty, I started it up with one stick and had the same problem, replaced it with the other and it was fine.