Hello saivikas! Your System Specs uses a motherboard from ASUS which has "onboard" graphics from Intel which is the 915GL chipset.
Unfortunately, Intel no longer supports that chipset. You might trying to get an update from the Windows 7 Update feature or from the Device Manager and clicking on the VGA Adapter listing trying to update the driver from the "Update Driver" button feature.
Your motherboard is quite old and it is perhaps a better setup for you would be to get and inexpensive PCI-E video card for about $35-50.
OR you can use the VISTA driver and install it this way, which is a "Copy & Paste from the Microsoft TechNet site:
Use the driver from vista, it will give the same results, use any driver backup program to export and save the driver, then reinstall the same driver in Win7
PS, you may need to install through device manager, you must follow these instruction or Win7 will not install the drivers as the generic drivers it uses by default has a newer date. Install by going to device manager -> right click on your display adapter -> select "update driver software" -> select "browse my computer for driver software -> select "let me pick from a list...." -> select "have disk" -> select "browse" -> browse to the folder where your device drivers are located and select the inf file and install the driver...