Help with BIOS update

I was given a gateway mx3215 laptop. I upgraded the RAM from 256mb to 1gb (which is the maximum ram capacity stated by gateway) however System properties only shows 448MB from which I know 64mb were subtracted for the video card to use(shared memory) (448+64=512) anyway is not reading the right amount of ram. CPU-Z reads the right amount of RAM 1gb. but I don't know what to believe. I was advice to do a BIOS upgrade put it has being kinda hard to find out the motherboards make and model my chipset is a VIA vn800 but CPU-Z says my motherboard is "gateway" make. nothing else. AIDA32 says the same thing. and gateway website doesnt offer a BIOS upgrade for this computer model.

Feature Description
Processor Intel® Celeron® M Processor 360
1 MB L2 Cache | 1.4 GHz | 400 MHz FSB
Display Screen 14-inch Widescreen Ultrabright WXGA TFT
Chipset Via VN800
Memory 256 MB DDR2 (1 × 256 MB) SODIMM (PC4300). Expandable to 1 GB
Video S3 UniChrome™ Pro Integrated Graphics Processor
Up to 64 MB Shared Video Memory
OS WinXP 32bit SP2


any suggestions about the RAM or the BIOS update would be greatly appreciated!

I have the exact same computer with same specs and same problem. I have tried to upgrade RAM from 256 to 1 GB. I have tried Samsung (brand of original 256 RAM), Crucial, Kingston, KByte, Corsair, Patriot, and PNY and my laptop will not recognize any of these. I get a black screen. Specs state can upgrade to 1 GB. This only has one slot and when I put the old 256 RAM back in, computer works. PLEASE help!

Feature Description
Processor
Intel® Celeron® M Processor 360
1 MB L2 Cache | 1.4 GHz | 400 MHz FSB
Display Screen 14-inch Widescreen Ultrabright WXGA TFT
Chipset Via VN800
Memory 256 MB DDR2 (1 × 256 MB) SODIMM (PC4300). Expandable to 1 GB
Video S3 UniChrome™ Pro Integrated Graphics Processor
Up to 64 MB Shared Video Memory
OS WinXP 32bit SP2