What if i have 3 dependants on my W4 and cannot claim them when it's time to do file my taxes?

[AnthonyC]

If your withholding all year has been reflective of claiming 3 dependents and you are not able to actually claim those dependents on your tax return, then it may mean that you will owe taxes or receive less of a refund than you are expecting.  Your withholding will be less than it should be and if you don't have the dependent exemptions and related credits to offset - this will likely cause a rise in your tax liability.