normally this is linked to low memory in just one sector your useing. so each can be checked.
by removing files you are not useing,and transfering others into the one with space, also run disc cleanup will give some extra space,as will defrag.( this may not work untill you can clear some space)
by the fact that you are refering to problems with the programs,Id suggest a spyware scan,
running such actions on a regular basis I find is a must