after updating avast my computer does not boot

[fierogt]

I have a notebook computer and after updating avast home a restart was required. However the computer will not go into windows in any mode (safe or normal) it goes through the boot process but never enters windows. I have windows xp home edition. Can you guide me in the correct direction?

[Spiritsongs]

   Hi :

     Did you do a PROGRAM Update or a DEFINITION FILES Update ? Sounds like a "Program" Update,
     since a restart was necessary !? Do you from what version to what version the "Update" was
     done ?  Assume you do NOT have any other antiVIRUS program on your "notebook" !?

[fierogt]

It was the very lastest program update and I do not have any other virus program on the notebook.

[Lisandro]

Sometimes, the only way to boot is overinstallation...
You won't lose your programs, settings, data, files, etc.
http://support.microsoft.com/default.aspx?scid=kb;EN-US;315341
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q314058
http://www.webtree.ca/windowsxp/repair_xp.htm

You may have to (re)install some applications though, but that would be all.
You will still have all your data.