Acer Aspire 4720z display problem

Hi all I am new to this forum.
I have one Acer Aspire 4720Z laptop. It shows bios and after that it goes to black screen. I thought it was operating system problem then i tried to install new operating system. When I tried to install fresh operating system it shows me press any key to boot from cd... and i press key but the screen goes blank again. I tried to connect to external monitor but the problem is same. It goes blank after booting from cd on external monitor too.
Somebody suggest me to reset bios but I don't have service manual of this laptop. bios shows me these information
I have phoenix trustedcore(TM) bios system bios version is V1.3709
VGA Bios Version: SantaRosa 1478
System Memory:640KB
Extended Memory: 1014MB
Video Memory: [8MB]
Its display adapter is upto 252MB Mobile Intel Graphic Media Accelerator X3100 is my laptop graphic.
Pentium dual core processor T2330.
I tried to load default setting but the problem is same.
Please help me to solve this problem.
BR
Prasanna from Nepal

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