"No Sync" on a Sony PVM-14N5MDE when booting into Windows 7
 

I picked up an old medical monitor and a pretty cheap HP PC with Windows 7. The computer has an 8600GT with S-Video output which worked with the PVM before. Sadly, the HDD in the computer was on its way out so I had to replace it but now when I try to boot into Windows 7 I get a "No Sync" message from the PVM and obviously no display.

It displayed the OS on the old, dying, HDD so I plugged it back in, albeit with the SATA and power still connected to the new drive, and I had the same issue again. At first I suspected it was some kind of driver issue i.e., no NVIDIA drivers meaning no analogue signal from the card in OS, but now I can't figure out if the PVM is at fault, software, or the GPU. Perhaps Windows 7 by default outputs a resolution the PVM can't process?

I should also mention that the computer and PVM have no issue displaying the BIOS, it just displays "No Sync" when Windows loads.

If anyone has had a similar experience and knows what's going on, I'd really appreciate it!

Have you tried running in "safe" mode?

Yeah, I just got an infinite loop of first time setup or something.

Funnily enough, I just tried a Vista 64-bit install and that seems to have done the trick. I'm not sure if it's some kind of compatibility issue, or if HP did some weird stuff with the BIOS. Either way, I'm on an even more outdated version of Windows now, but the monitor displays on boot.

If the old HDD is still bootable and the data on it isn't corrupted I would use clonezilla to make a bootable copy of it and use the copy.
For old HDDs that may have unobtainable drivers on them it's a good idea to use a tool like clonezilla to make a backup image of the entire drive on a separate drive that you can reimage onto a new drive if the original dies.

If it's beyond any of that helping I'd try to make windows 7 update and get better drivers then I'd hook up a second VGA/DVI/Display Port/HDMI monitor (whatever newer higher rez output connector the graphics card supports) boot with only the newer monitor connected then right click on desktop select adjust screen resolution, detect additional monitors figure out which is the S-video output and try adjusting settings on it till it syncs and looks OK. It might have drifted into PAL mode when you're using an NTSC monitor or vice versa.