jumping curser

I do not have a touchpad. I have a Dell Inspiron with Windows 7. I
have had to replace the harddrive twice in this machine in 2 years due
to fatal crashes. The new harddrive was installed less than 2 weeks
ago. Since the installation, my curser moves itself, seemingly at
will, while I am typing. Almost every other word has to be altered due
to the curser moving to another spot. HELP PLEASE