large file fragmentation /not clearing all the time

Hello..i have been using defraggler for a couple of years ,no problems at all generally !! ,normally 3/5% file fragmentation 10/15% if i am busy ??.........................recently 15% file frag ! it took 15.5hrs to defrag/shutdown..........ran the defraggler prog next day to check it out ran analysis showing 18% defrag ??computer had not been used since that defrag ???now after A couple of days of ...just doing emails not much else.....analysis shows 29% defrag it will take a couple of days to clear this ....do not like the computer left on for this length of time ..........................can anybody offer any help ..please

running windows xp home ,160gb...h/disc..1.256gb memory Mozilla web/mail system......cannot find any answers your web site............................but various posts on this forum reflect similar

thank you....... jewells .............