power supply?

HI,
I recently purchased a power supply from the shop called The Nuthouse In the arcade in Abertillery, the persons name I purchased it from is Martyn Barlow which is the owner of the shop. The phone number is 01495 215577.
This is the second power supply I purchased from this shop and both have not lasted 3 months. The proprietor contacted you regarding these complaints and I was informed to contact you myself.
The model number for the last power supply I purchased is KY2500ATX-450W P4 which is not working.
Please could you contact me to find out how to replace this power supply at my following email address wales4us@hotmail.co.uk
Thanks
Raymond Thomas