You would have to inspect each control to see if they picked it. like:
On Search_click()
Code:
dim sSql as string, sWhere as string
if not isnull(cboState) then sWhere = sWhere & " and [state]='" & cboState & "'"
if not IsNull(txtName) then sWhere = sWhere & " and [Name]='" & txtName & "'"
if not IsNull(chkContact) then sWhere = sWhere & " and [Contact]=" & chkContact.value
'remove 1st And
sWhere= mid(sWhere,4)
sSql = "SELECT * FROM tblCompany WHERE "
sSql = sSql & sWhere
frmResults.Recordsource = sSql