I think I have solved the problem disscussed in my last post. However, I have made a mistake. I have configurate my boot.ini like this:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect
I can not restart my computer when I have done that on system. The reason is that if some of the critical windows start up files can't load in the initial 1GB of memory when you boot in 3GB mode, windows won't start at all. If you DO get errors trying to boot up in 3GB mode, reboot in 2GB mode (default) and reconfigure the boot.ini file. You may just need to edit the 3GB option to use only 2.9GB or 2.8GB RAM, to allow your operating system just that bit more kernal address space.
So we should change boot.ini file to:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOW S
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Micro soft Windows XP Professional" /fastdetect /NoExecute=OptIn
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="XP Professional 3GB switch" /3GB /USERVA=2900 /fastdetect /NoExecute=OptIn
This time when you select the 3GB option, the USERVA will tell the system to allocate 1.1GB to the operating system and 2.9GB to the applications. Configure as necessary (changing the USERVA to 2800, 2700, etc), until the 3GB option works.
Also MS tells us how to enable 3GB and use USERVA, Memory Support and Windows Operating Systems
But we should avoid to set 3GB swtich in windows xp system. Since it is known that some plugins can not work properly, for instance here Plug In Issues.