I have just rebuilt my mother in law's HP Pavilion a1108 using the recovery partition (Windows XP Home). Everything was fine until I installed SP3. Now the machine won't boot except into safe mode.

Hi,Are you using an AMD processor?Step 1:As you are able to boot to the desktop in Safe mode, Put the computer in a clean boot state and check if the issue persists.a. Putting your system in clean boot state helps in identifying if any third party applications or startup items are causing the issue.b. Refer the following Microsoft KB article for more information on how to troubleshoot a problem by performing a clean boot in XP:How to configure Windows XP to start in a "clean boot" state?http://support.microsoft.com/kb/310353Note: After troubleshooting, make sure to put the computer to start as usual as mentioned under the section 'Steps to configure Windows to use a Normal startup state' in the above KB article.Step 2:a. If the issue still persists, then disable automatic restart so that we get the complete error.b. To disable automatic restart on system failure, boot into advanced startup options and select ‘Disable automatic restart on system failure’ and hit enter.c. This Prevents Windows from automatically restarting if an error causes Windows to fail.Error message after you upgrade a computer that uses a processor other than an Intel processor to Windows XP Service Pack 2 or to Windows XP Service Pack 3: "STOP: 0x0000007E"http://support.microsoft.com/kb/953356Regards, Manasa P – Microsoft Support.