Check to see if you have PAE installed on your CPU using CoreInfo, The * character indicates that are included and the - character indicates that are not included, Download now: https://www.dropbox.com/s/vm3jlukggapan1e/CoreInfo.zip?dl=0
Run set.bat then copy all of the text to the Text box of Reply at the end of the page.
If PAE is enabled on your system, Get 64-bit, If PAE is compatible but it's disabled, Go to Run and then type "NOTEPAD C:\BOOT.INI" and press Enter, On the [operating systems] part, You should see this:
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect
Change it to:
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect /pae
Then save it in CTRL+S, Restart your computer, After restarting, You should see in System Properties main menu PAE on the bottom of the RAM: Physical Address Extension, like this:
If your CPU does not support PAE, while your CPU gets a 64-bit, Get a 64-bit OS.
If your CPU does not support PAE, and not support a 64-bit, Get a newer OS.