problem displaying PC via HDMI with Onkyo 705

Ive been using my HTPC via a DVI to HDMI cable plugged directly into my toshiba DLP tv for some time. Recently I purchased an Onkyo TX-SR705 receiver for it's HDMI switching. Im running a directv box HDMI in, Sony changers component in, and outputing everything through HDMI. I hooked the PC DVI to HDMI cable into one of the receivers inputs, but I cannot get the PC to display. Ive tried 800x600 and 1280 by 720 resolutions and accessed the Onkyos hidden men to force the output to 720p with no avail. I get a flashing HDMI ligh on the receiver and what appears to be fine grained snw on screen. All other sources (than the PC) work fine switched through the receiver. he Tv only has one HDMI input so after all the costs, I'd really like this to work so I dont have to rewire back to component for everything.

I've tried both the settings offeed for HDMI on the Onkyo one is locked to 720P, the other is "Auto" neither made a difference,

I can run any resolution I like from the HTPC to the television. The TV just shows me different sizes of desktop. 800x600 has worked the best, filling the screen with no overscan. I tried 1280x720 but there was massive overscan in all directions.

The Toshiba is a 62hm84 720p only. The drivers are catalyst from around three years ago, havent messed with them since setting the system up. I did have some issues back then with black screen when switching inputs on the TV requiring reboot of the PC to get picture back, but the version of catalyst im using now resolved that.

Audio coming from soundblaster 5.1 Analog to receiver.

I dont recall the exact video card model other than I believe it is a fanless radeon of reasonable specs from three years ago.

Thanks a bunch for the replies guys. RE the question about the hidden menu, if you Hold AUX and POWER buttons on the front of many of the receivers, it opens a menu where you can adjust the properties of the HDMI output including contrast brightness and resolution.

I checked my video card and its a radeon sapphire 9600 with DVI and VGA. I purchased it at the time because it was the best fanless card I could find and my case is a cool power HTPC and its kinda weird and tight.

Im downloading drivers now, but looks like a new problem. Cat9.6 Drivers require .net2.0 and for some reason microsoft wont let me connect argghhh.