Screen flickers for a long time on every start up

I've never had a similar problem before. It started about 2 weeks ago, upon turning on my pc or waking it from standby the screen would flicker (~4 seconds of black/off, ~0.5 seconds on) and this went on for a minute or two. After that, nothing happened until the next time I turned it on or woke it up.

However, the time it takes for the flickering to stop has been increasing and last night it took nearly an hour, today about half an hour. My monitor is a Samsung SyncMaster 206BW, and it has a little blue light around the on button - the light turns off when the monitor turns black during the flickering, and it shines blue for the half second or so the monitor is on.

My video card is an Nvidia asus gtx 460

I'm not sure whether the problem is with the monitor or the videocard. The cable connecting the monitor is a large white one, not the usually blue 'RGB-in'.

Things I have tried: restarting everything, replugging all cables, plugging them in different sockets (even used another socket of my videocard since it has 2), installing the latest nvidia updates, etc.

Oh and lastly, I'm using Windows 7 ultimate 64-bit.

I would really really appreciate any help, if you need any more information I will provide it!