Every computer is different, when you first turn on the computer it should tell you what button to push to enter the BIOS. It's usually one of the following and you must push it within the first 5 seconds: F1 F2 F10 F12 ESC DEL
Once in the BIOS you have to find the menu with memory remapping, it's different on each computer and enable it.
Try this as well:
1. Click Start. , type msconfig in the Search programs and files box, and then click msconfig in the Programs list.
2. In the System Configuration window, click Advanced options on the Boot tab.
3. Click to clear the Maximum memory check box, and then click OK.
4. Restart the computer.
Peace.