My computer's playing up smart people help me!

hi my computer’s confusing me i can go on Mozilla Firefox and use the internet and my computer says its online but msn, ea download manager, internet explorer and pretty much everything else says I’m offline.
what can i do to fix my computer???

and here’s the thing that i think is f-ing it up my hardrive that is in this computer is from a hp and this computer that its in now is a Acer would that have anything to do with it?