Error 404

I appreciate this an old laptop, (was my youngest son's) and well used and probably abused. I think I've caused this problem by not uninstalling programs properly.
Can't really afford to pay for a solution, thought you guys might be able to show me a way to fix these faults.
Error 404
Explorer not working (tells me not connected when I know I am.)
Is there anything you would recommend (not bin it :-) that might help?
Thanks in advance,

Mike'