|By "anti-virus" do you mean MalwareBytes?|
If so, were you able to get to Windows to attempt to install it?
Does this blue screen give any other information, if so let us have any numbers or file names it refers to?
Have you an XP installation CD or restore CD?
Has anyone else had access to the computer?
What were you doing immediately before the problem came along?
Please give us the make and model number of the computer.
I might turn out that you have a problem on your hands that could prove tricky to fix with help from afar and could require a fair degree of competence on your part. We would also need to backup your important files first - can explain later if necessary.
Even if you should resort to taking it to a workshop to get it fixed it would still be a good idea to back up your own files first - they will get lost if they choose to re-install.
Always pop back and let us know the outcome - thanks