|Wow, that's a lot of processes running, and a lot of programs launching at start-up. |
For testing purposes, disable everything in your start-up, except anti-virus.
To trim down your running processes, go to Black Viper's XP Service Configuration page (for your installed service pack, e.g. SP1, SP2, or SP3) and set everything according to the "Safe" column on that page. This will disable a lot of unneeded services/processes from running in the background. This is one of the first things I do when setting up a new machine. Note, you'll probably have a few that are not in his list, due to programs installed on your machine.
Once you have the start-up items disabled and the services/processes trimmed down, try it out and see if it has helped. I'm sure it'll at least boot quicker than before.
After re-reading your original post, I realized that I missed the bit about not booting to the POST screen, after being shutdown awhile. This sounds to me like a CMOS battery problem. If you can enter the BIOS, are the drives listed, and is the date/time correct? If the battery is dead/dying, the CMOS loses data, resulting in Date/time setting back to factory and hardware (drives, RAM, CPU, etc.) needs to be detected again.This hardware detection is vital to the BIOS being able to POST. You may even find that your CPU is running at a lower speed, due to lost FSB settings.
Please let us know if you found someone's advice to be helpful.