PC rebooting by itself

If the PC is self re-booting when booted from a floppy disk, or the XP CD, then you have a hardware problem.

The power supply may have chosen this moment to get weak, and is shutting down from excess current draw.

It is also possible that the modem has a hard failure from a lightning storm that hit the phone line. (Lightning damage can show up weeks after the event.)

If you have a spare, swap in a larger power supply.
If not, try removing ALL plug in cards, unplug USB devices and unplug the power cord from extra drives.
If the system now boots properly from a floppy, you have the hardware problem corrected.

Now, depending on how Me was installed and removed, you may still have a problem booting into XP.
There are a number offiles that XP requires be in the root folder of the boot drive.

boot.ini
ntdetect
ntldr

If these files are missing, XP cannot load.

except for boot.ini, you can copy these files from a PC running XP.

boot.ini can be copied, but may need editing to point to the correct folder where XP is installed.

Chas

I had a problem with a pc constantly rebooting itself and it turned out that the RAM was bad.

I have the same problem once ... what i did was i just reformatted my hard disk then reinstalled windows... changing from WinME to WinXP may have corrupted your Windows files..
If you want to install Windows XP,i suggest that you don't partition your harddrive because WinXP want the whole piece of your harddrive if you partition it,it may not install properly.