Display quivering and screen changing size...

I put a machine together 3 months ago and it has been working flawlessly since. I am not overclocking anything and I do not get blue screens or shutdowns, but the screen will distort a bit, even just the desktop when nothing is running. What happens is the screen will seem to move away a bit from the corners and boarders. It might concave in a bit on the sides for a moment, but then goes back to normal. It happens more often now and occasionally it will look like the monitor is going to shut down and the picture gets small on the screen (takes up about half of the monitor, but centered). It goes back to normal after a bit, but it seems to be getting worse.

My monitor is an 17 " Insignia, and it is about 3 years old. The computer hardware is as follows:
GIGABYTE GA-P35-DS3L LGA 775 Intel P35 ATX, Intel Core 2 Duo E6750 Conroe 2.66GHz LGA 775, EVGA 256-P2-N751-TR GeForce 8600GT 256MB 128-bit GDDR3 PCI Express, Western Digital 80 GB Drive, G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit, Sony NEC Optiarc Black IDE DVD-ROM Drive, Thermaltake Tsunami case, ARCTIC COOLING Freezer 7 Pro 92mm CPU Cooler. Antec Earthwatts 380W PSU.

I'm running Windows XP home version and display is 1024 x 768.

I'm kind of guessing it might be the video card at this point, but would like some opinions about it possibly being a PSU without enough output or a motherboard short.

Thank you for your responses.

I am gonna assume LCD monitor since you dont specify otherwise..sounds like its failing.

it is definately failing if the monitor is a CRT.. thats classic symptoms of bad caps or failing solderjoints in a CRT monitor, specifically the horizontial size circuit, which controls size, and pincushion

17 " Insignia can be a CRT as well as LCD.

? Which one.

IF CRT the monitor is failing.

Time to buy a new lcd!

Your CRT is toast!

^ I recommend getting a BenQ monitor... I don't know if you game or not... but I just got a 24 inch benq monitor... picture is amazing.... and got it for 300 at neweg... so for relatively little you can get a great monitor... if you don't game I highly recommend it because it is very nice and can actually make surfing and what not easier

if you do game... i'd probably get a nice 19" 1280 by 1024 monitor because your gfx card probably can't handle much more than that in games