Dell 5150 dimension; windows XP sporadically reboots on it's own.

SOURCE: Multiple viruses on a Dell Dimension 1100

Formatting your hard-drive is the easiest way to eliminate anything on that hard-drive. Follow my steps below to do just that.

Start your computer so you can open the CD-ROM drive. Insert the Windows Installer into the CD-ROM drive. Close your CD-ROM Drive. Shut down your computer.

Now start your computer and while your system starts up look for an option for the, "Boot Menu" or, "Boot Device." It will have a key associated with it that you have to press continually for you to enter the menu. For instance:

(F8) Boot Menu.

Here's a hint to help you out. If you see the loading screen of your operating system, you've missed your window. Restart and try again.

Now just to clarify, we're not out to change the boot sequence, we're trying to boot from a specific device. Once you find that menu select your CD-ROM drive and press enter. It might ask you to, "Press any key to boot from CD-ROM drive." As it mentioned, press any key. Afterward the Windows Installer will launch.

Follow the directions on the screen to set up Windows. Yeah, it will warn you that there is another OS installed on your primary Hard Drive and that it might be better for you to, "Repair" your system. Ignore that and continue with the process to Install Windows. Before the final step to install Windows there is a screen that allows you to partition your hard-drive. In this are, erase ALL partitions. Afterward create a new one which will be your C:\ drive. If you want to partition your drive further, go ahead. However, at this point you can continue the Windows Installation and the Installer will ask you if you want to format with the NTFS or FAT32 type. Format with the NTFS type.

Now the Windows Installer will erase EVERYTHING on your hard-drive and proceed to install Windows XP.

SOURCE: Missing Windows XP Product Key-Need to Reinstall/Repair XP

I'm assuming you have quite a lot of computer savvy??? You'll need to access that drive and get the original key off it. Try connecting the drive to another pc and see if you can get to the Windows folder. Once there, use Jellybean Keyfinder to navigate to the Windows folder in that drive and take note of the OS key. From there you can reformat and use the existing key.

SOURCE: Dell dimension 3000. Just Black Screen no Windows XP.

From your description, you were able to boot the machine properly in Safe Mode. While in Safe Mode, change the video resolution to the lowest possible (color depth does not matter at this point). You should also check that you are configured for single monitor operation if your video card supports multiple monitors. Reboot the machine normally. If all goes well, you can readjust your video settings for a higher resolution again.

SOURCE: dell dimension 5150 ethernet problem

Okay, so it seems you installed Microsoft Windows XP Home on a what was Media Center Edition installation, and the ethernet is no longer worker.
Please refer to dell.com's support section, enter your model, and download drivers that you need.
To find drivers you need, Go to start --> control panel and then go to (under classic view) system --> the hardware section, open up device manager, and then look for ones with a yellow big question mark, and get those drivers from dell's website. Burn these drivers to a CD on another computer, or use a USB flash drive if that does work.
Good luck.

SOURCE: Can't start Windows, Blue Screen gets in the way.

can you press the function key that takes Windows to diagnostic mode - usually F8. You have to press this key very quickly after you power on.

This might help you understand where it is failing.
Hopefully you have a recovery CD with which to boot and test the hard drive for corruption.
You will need to setup the BIOS bootup sequence to go to CD first.