Format a Compaq. I have a 5 year old Compaq Presario sr1430nx. Getting slow Probably full trash. I

Question

I have a 5 year old Compaq Presario sr1430nx. Getting slow Probably full trash. I would like to format DH start over Like new. I did a recovery once, didn't help. I made copy's of the start up disc like I was instructed to do when I got it.. could you suggest what I need to back up? I bought a BOOK external HD for back up.. Thank you for any HELP.. Randy