Goodmans LD3260 TV?

Hi. When switching on my tv it makes quite a loud buzzing sound (displaying black screen) after 5 seconds or so picture the flashes on screen for just 1 second and then goes back on stand by! After 10 attempts at switching it on (with mostly the same result) the tv may suprise me and display the desired channel BUT only for 30-45mins and then switch itself off and go back on stand by!!!! hugely frustrating!!!!! Any ideas what the problem could be and is it worth fixing or purchashing a new tv???
Thanks Nat