PC graphics issue(s)

I've been having issues w monitor display dimming and slight flickering - the issue is resolved by switching to lower resolution. This sucks, so my q. what is the source of the problem - is there a trick to overcome this or only a new Graphics Card will do. If it's the latter, I'm not a gamer so I would like to purchase el cheapo Card that will handle, say "heavy graphics" - such as multiple stock charts displayed - hope someone can recommend a $10 smth. (AR?) Card that should put this to rest. To help with advice I'm providing what I hope is helpful info - if smth. important is missing please let me know.
TIA!
PC: Acer Aspire3400
AMD Athlon II x2 215 Processor 2.7Ghz
4GB RAM
ATI Radeon HD4250 Graphics
Monitor HP S2031 => 20". Recommended resolution (the one that's giving me hard time 1600x900).

Thanks for the input:
Checked all drivers prior to posting - no updates
Monitor is hooked up to PC the "basic" way (no DVI/HDMI..)
Replaced the monitor cable per LiquiedRetro suggestion and that seems to have made the difference - however I'm still cautious since in the past things looked well then suddenly revert to bad - if so, I'll report back - thanks again all.

Have you tried updating the drivers?
Maybe switch the DVI cable as well?

I have two HD4250s in my desktop right now as well. Was thinking of upgrading them, but no point.

Are you sure that the monitor is not to blame?

$10 graphics cards are hard to come by, $20 is doable after rebate. A few things to try first though that are free. This does sound like a GPU issue though, similar to one I had about a year ago, but I did not try the lower resolution thing.

#1 Try a different monitor/cable/input. Borrow one if you have to. Make sure connections are tight.
#2 Download new graphics drivers from either ATI or NVidia, whichever you have. Uninstall the old, reboot and install the new.
#3 Open up the computer, and dust the insides out with compressed air. This will solve any heat issues you might have.

check the refresh rate too