"Phone up your BB supplier and ask 'em why. "
Eh??
Why would they have anything to do with a computer running slow?
If it's 4-5 years old it probably has the bare minimum of RAM in it for a system today, you also probably have accumulated loads of junk installed that you don't need.
so, check the amount of RAM you have, if less than 1GB you should consider upgrading the RAM, also uninstall all unused programs and junk that will be installed through add remove programs, then run a full defrag on the hard drive about 2 or three times.
Also as Galack says, run full scans with both your antivirus, and even more importantly malwarebytes to ensure that the system isn't running any nasties in the back ground.
If it's still running slow after that then it's time to look at the startup processes and see what isn't needed and disable anything that's not.