How to keep TV working as PC monitor w/o turning off PC?

I have an HDI-HDMI connection from my desktop to my Sanyo plasma big screen. Everything works well until I turn the tv power off. When I try to turn the tv back on and use it as a monitor, it just gives me a black screen. The only way to fix this is by rebooting my computer. This is an annoyance to say the least. There's no other monitor in use, just the tv. How can I get my tv to work as my monitor constantly, without turning off my computer?