It will repair any operating system errors on the hard drive. When files are fragmented, it takes the operating system longer to open them. Defrag helps your system operate more efficiently. Scan computer for Viruses. Viruses can cause system errors.
Viruses can cause hardware to function incorrectly.
Update your anti-virus files monthly. System freeze-ups can be due to having a dirty computer. Dust and dirt have a tendency to generate heat which cause many of the intermittent errors associated with your computer. Pay special attention to the power supply fan and the CPU fan. If either of these are not spinning, have the machine serviced immediately.