That monitor should come with a 3 year warranty from dell.
I would suggest finding the service tag, (or "dell works order number" that is on a sticker on the original box), the serial number (on the back of the monitor) and the company name of the reseller you bought it from (unless you bought it direct from dell).
Then call them up on the dell technical support line (0844 338 1200) and ask to be transferred to the monitor section. Once there explain clearly to them your problem and be ready with the info I mentioned above.