How can i fix my guitar/amp?

I have had a marshall head with one fender cab unit for about a year now and sometimes when i plug the guitar into the amp no noise comes out at all, even if the volume is on full whack. I took my speaker unit into my local music store and they got back a week later and said they couldnt find anything wrong with it, but that i would need a proper speaker lead, as i had lost mine so was using a normal guitar lead. Even before i lost the speaker lead, often no noise would come out. When i got back home i used the speaker lead, but at first again it didnt work, and then i fiddled around at the back where the lead plugs into the head, and its started working, but now again its not. Whats more, i have always had problems with my guitar and its often been soldering coming loose around the jack, which i have fixed time and time again and its been fine, but now even with no soldering being loose or any visible problems, no sound comes out, even with a different amp, as the amp also doesnt seem to be working. Though it all may sound quite vague, if anyone has any ideas or information, please let me know. Thankyou, Tom.