Computer freezes continuously ..

Question

hi, why is my computer continually freezing up .. ie .. ok for maybe a couple of mins .. then all freezes for maybe 30 seconds .. and then ok for another couple of mins and so on .. getting very very frustrating .. i have cleaned all internet rubbish which continually arrives .. and this seems to make it ok for maybe an hour or so .. and then the same problem .. hope someone has some ideas / thoughts .. peter