connecting my laptop to my hd lcd. tv......help!!

please help...i have a sony bravia hd lcd tv and sony notebook...my tv has no pc connection so i have purchased a vga to hdmi lead (as advised by my local sony store)...i have plugged the lead into the hdmi input on my tv,gone to the hdmi channel on my tv and nothing is happening...im sure i have to adjust settings on my laptop but unsure of which ones....any help would be greatly appreciated!!!