You have two choices, as far as I can see.
1) Try backing up all your data to an external hard drive and then installing Ubuntu on your machine. This is a free operating system that would replace Windows. However, it's got less bulk than XP has, so should run faster. You won't be able to run all your windows software, but it does come with Firefox (web browsing), an email client, OpenOffice (Microsoft Office free replacement), as well as a host of other software.
2) Do as vehelpfulguy suggests, and buy a new machine.
The new machine is certainly the easier option, but it may well be worth trying Ubuntu anyway, just to see if it makes any difference.
With either choice, you'll need to backup all your personal files to another drive, so transfer either into Ubuntu or onto your new computer.
http://www.ubuntu.org