Do you know the specs for it?
Windows version?
Ram/memory amount?
CPU info?
Brand?- some come with a lot of Brand bloat-ware..
Hard drive size? is it nearly full or lots of empty space?

Have you tried a cleaner like Glary utilities-
http://download.cnet.com/Glary-Utili...-10508531.html

or ccleaner-
http://download.cnet.com/CCleaner/30...-10315544.html

both are free, I've used both of these for a long time.