64 Recognizes 4Gb But Only Uses 3Gb!!

hi to all and tnx in advance for support,i've installed 4Gb RAM on my Notebook Toshiba with Intel T5500,Northbridge Intel i945PM rev. 03 and Southbridge Intel 82801GHM (ICH7-M
DH) rev. 02.

After memory update i've installed *Vista x64 Ultimate SP1* and System Info under Control Panel says 4,00Gb Ram Memory but *Task Manager says only 3069Mb Physical Memory*.

Moreover i ran msconfig and deselected MaxMemory flag in Advanced Options under Boot tab (as i saw somewhere on internet )but nothing changes. The bios recognizes correctly 4Gb, and programs like CPU-Z recognizes 4Gb, but msinfo says:

- - Installed Physical Memory (RAM): *4Gb*-

- - Total Physical Memory: *3Gb*.-