How do I get an external monitor to work?

I have an Acer Aspire 1640z and my screen is broken. I have it hooked up properly to an external monitor (a rather old one, but it still works) and when I turn on the laptop the boot screen appears on the external monitor then the monitor turns off as soon as it is booted. I have tried the Fn+f5 thing. (As well as Fn+every effin' key imaginable) and it still will not work. Any ideas? I really do not want to throw $200 into a new screen for an old, crummy computer when I know I'll get a new one when I graduate college in a year.