Can't complete XP Home re-install

Hello,
My computer has been hijacked by continuous pop ups of dialog boxes that are titled: C:\WINDOWS\system32\cmd.exe. I tried to do a system restore to a previous date but that didn't work. So I am now trying to reinstall XP Home but after running the disk and the computer restarts it opens to blank black sceen and the install never completes. Any advice? Please keep it simple for me to understand.