XP will not boot up period it goes to a blue screen that say check for virueses on your computer. Remove any newly installed hard drives or hard drive controllers. Check your hard drive to make sure it properly confirgured and terminated. Run CHKDSK /F to check for hard drive corruption, and then restat your computer
It could be a variety of issues, i.e. malware, bad HDD, etc... First though, try and run a startup repair from the XP disc or recovery partition. Next, if you can boot into safe mode, run a virus/malware scan and see if it comes up with anything. If it doesn't find anything and you have another computer around, download Seagate Tools and install it on the laptop in safe mode. From there run a scan to see if anything is wrong with the HDD.