Windows rebooting repeatedly at startup, later every few hours

I'm in Europe.
I've read all the typical advice for automatic rebooting.
It's early spring and there is no overheating of my CPU.
I've uninstalled the Akamai software (provided with Adobe Flash Player), a possible cause of the reboots.
I've reinstalled the Flash Player software.
The problem persists, however.
My computer is 6 years old, Windows XP, no repairs during that time.
I just can't put my finger on the problem.
I've attached two dumps from today and three from Friday when the real problems started - I mean 5-6 automatic reboots, especially at startup, which sometimes end in success and sometimes in a still screen of uncompleted startup.
What do you think?

What antivirus program are you using? Looks like a Norton product. Is XP updated to Service Pack 3 and beyond?

the following

Norton Internet Security 2012 (which wants the Windows Firewall to be disabled) and Windows XP Service Pack 3

Remove Norton and install Microsoft Security Essentials (MSE):
http://windows.microsoft.com/en-US/windows/products/security-essentials

Before you complain about having to remove Norton, be aware that it is most likely contributing to your computers instability... Let MSE control the Windows firewall

Norton

I've been using Norton products on this computer since 2006 without problems.

I haven't used Norton since 2006! I told you that Norton is contributing to your computers instability. If you want to leave it that way, so be it