It's probably just a simple fault, and if you're really that clueless about electrics then it may be cheaper to get in a professional, at least it will save you funeral expenses and the like.
Nontheless, you came here for help and so I'll try. Is all your lighting fed off one fuse/MCB, or is it protected by multiple fuses/MCBs, i.e. one for upstairs lights and one for downstairs?
If it's all fed from one protective device, you have a break somewhere in the circuit. As you're not too confident I'd recommend you isolate EVERYTHING at the consumer unit/fusebox via the main isolator.
If you've drilled any holes in the wall recently or hammered in any nails then you may have gone through a cable, in which case you certainly need to call in an electrician. However, you may just have a loose wire at a ceiling rose or light fitting that has broken the circuit. Start by inspecting any fittings you've changed recently and look for loose connections, there is no need to check behind the switches if the circuit is wired in the usual loop in/out the ceiling method.
Don't go poking your screwdriver or fingers anywhere without proving dead first. You'll need a multimeter, voltage probe or similar (NOT a neon screwdriver) to prove that everything is dead before tinkering, which you can do by putting your test probes between live (red or brown) and neutral (black or blue) as well as testing both live and neutral to earth (green & yellow). Once again, I seriously advise isolating the entire installation before you start work. If you get the wrong circuit and you have an intermittent fault then a wire may appear dead when you test it, only to bite you as soon as you touch it!
Without more information from you, there's little more I can say.