Within a reasonable space of time you can request a refund, but this reasonable period is disputable. If you wish to take it further, contact their customer services as Currys and Dixons are getting more flexible over the 28 day rule (which is their own but the same as many other companys').
Under the United Kingdom's Distance Selling Regulations, you have the right to cancel the contract for the purchase of any items within a period of 7 working days, beginning with the day after the day on which the item is delivered.
The above covers you if you have changed your mind and does not replace the Sale of Goods Act.
Your Philips LCD portable TV having failed so soon is not of merchantable quality or fit for it's purpose. I would demand a refund and go elsewhere.
Also, click here;jsessionid=CxfvQPNXhspmyklK3BL3jM9MbntX73F1rgN23JnC7QJ6Rjg8zQ7h!-1880293289!1110564642699?r.l3=1074027367&r.l2=1074400662&r.l1=1073861169&r.s=sc&type=RESOURCES&itemId=1073792524 this describes the law from the seller's point of view.
In the event of a faulty item the retailer has the right to attempt to fix it first. If this fails a refund is in order. Philips are usually ultra reliable and I am sure the fault will prove to be minor.