Is this a PC or laptop?
If it is laptop then they should all work and I doubt if there is too much you can do if they dont work due to the size of the laptop case.
Is it a desktop computer you have built, or someone has built for you?
Some desktop PCs have USB ports at the front and at the back.
If someone has built a computer for you (or even if you bought it from a company like Dell) then it may be the USB ports were not connected up so it may be a simple job for someone to open the case and connect them for you.