Do you mean your motherboard is GA-7VA? There should be a jumper called the SW1 switch on the motherboard. The default setting is 100MHz. You need to set it to Auto, which will automatically detect either a 133 or 166 MHz FSB.
The 2500+ Barton should be 166MHz x 11 = approximately 1833MHz. It is now likely 100MHz x 11 = 1100MHz. Consult you manual to change the motherboard setting.