Can you run task manager when freezing? If you can, tell me which process have 100 percent of CPU load.
Try run sfc /scannow to repaire your system files.

Do not format c under other system, you will lost important file which will cause your windows can not boot up.
You can delete all file in disk c:, and windows will prompt alarm message to tell you...

After you install the windows xp, the default user is the name you input and the passworld is blank, unless you change them