Help my computer at home keeps freezing

I have a compaq presario with window ME installed. I have 128K RAM. The computer keeps freezing for about 15 seconds and then it starts up again. It does this in every software application. I have run scandisk. I have run Mcaffee virus checker. Ialso use norton cleansweep to clean unnecessary files. Could i have deleted something important? Is it a memory problem? Please tell me I don’t have to format the hard drive and start from scratch.