My dad started it up this morning and its really slow i clicked firefox like 20 mins ago and its still not popped up.

He also said a message about high memory usage or something came up.

Its about 5 years old, so anyone got any idea's how to get it back to speed or has it copped it?

I would recommend a full system reinstallation. Usually the best bet to clear out the accumulated 5 years of junk.

can you do that though the computer. dont think we got the discs anymore.

Some laptops have a recovery partition instead of an installation CD. You should have some kind of manual with instructions, alternatively you could google the model of your laptop and try to find instructions online.