^ It's F8 to get Windows boot options (like safe-mode)? The boot menu is usually about order of devices to boot from. Or are HP's really that back-asswards?
No, you are correct. F8 is used to get into the Windows boot menu for selecting things like SAFE MODE. ESC is used to get into the diagnostic menu for things like running hardware checks and editing the BIOS.
I didn't really flesh out my thoughts all the way. Here's what I would do:
- Hit the "ESC" button and then when presented with a menu, select what's available for hardware diagnostics in your computer. You should be able to run a test to validate various things like memory.
- When the computer is in this constant rebooting mode, try F8 to get to SAFE mode and see if it can fully boot. If it can't, then there's most definitely a hardware related issue going on.
- Does the computer feel like it's hot or uncomfortably warm? If so, perhaps it is overheating (although that's usually more of a problem for laptops than desktops). There could be a few causes for it, like compromised heat sink or decayed thermal contact material. Do you have a high powered graphics card installed?
- Let your computer sit for a few hours, then when you boot up and can get to the desktop, download a temperature monitoring utility. There are plenty of free ones available for download. When running, if your CPU or GPU is tending to jump above 90C, then it may very well be an overheating problem. You may have an option to control your inboard fan at the BIOS level--I'd select it to always be on.