Graphics or monitopr problem

I built my computer about 4 years ago; everything has been working fine but over the last month or so the display has got 'shaky'. The problem seems to be getting worse. It is like horizontal lines across screen, screen jittery.

I asked a local PC repair shop, they thought it was classic signs of the TFT monitor decaying. I bought a new monitor but problem just the same, if not worse as new monitor is wider screen. Also is very jittery when I can hear hard drive or processor being accessed. Just in case overheating problem I have thoroughly cleaned inside case and components and checked graphics card connection and turned up case fan but still no difference. Is this a sign of graphics card breaking down? Any other ideas.

PC is
Motherboard ASUS A7V600
Processor AMD Sempron 2400+
Ram 2No Crucial 512Mb
Hard drive Seagate Barracuda 7200
Graphics Sapphire Radeon 7000
Previous monitor LG Studio Works 560LS
New monitor Hanns.G HW173A

Thanks for response.

No fan on card. Have tried reinstalling drivers, no different so will get new card.

However, motherboard supports AGP8x, shall I get same cheap card as I have (AGP4x) or get something a bit better. PC used only for 'office' applications, no gaming.