All of your old computer equipment can be disposed of via your local authority recycling facilities
See links below for more details:-
Some manufacturers such as Dell also offer to take back any old equipment when you need to dispose of it:-
In some circumstances I may also offer to take away any old computer equipment for you, this is then repaired/refurbished and given away to local charities and good causes
Make sure your hard disk has been removed and destroyed or securely wiped before disposing of your PC - failure to do this could mean someone else could get access to your files, passwords and other sensitive information - my advice would be to remove the drive and smash it with a hammer, this way you can guarantee no one will be recovering anything from it, as some so called tools which wipe hard drives don't always do a very good job and an expert in data recovery could still recover your files!
The images below show the usual location of a hard disk in both a desktop and a laptop computer