You've done everything , so answering these questions should be easy:
1. Why u no post system specs as asked in the "read before you post" sticky?
2. Is your motherboard BIOS up-to-date?
3. Have you tried fiddling with BIOS settings?
4. Does your card get enough power?
5. Are the card's clock speeds what they should be when you see this corruption?
6. Is this corruption desktop-only, or does it show up in 3D applications (games) as well? How about UVD-accelerated videos?
7. What happens if you move the card to another computer? Does it take the problem with itself?
8. What happens in a clean install of Win7?
9. What happens in a clean install of XP?
10. Linux + latest open source drivers - Does this combo work?
11. Linux + latest stable/beta proprietary drivers - Does any of these combos work?
12. Any anomalies in system (like OC, custom PCIe bus speed, custom voltages etc.)? Don't forget to include in #1.
CPU: AMD Phenom II X4 810 @ 3250MHz | RAM: Kingmax 2x2GB DDR2 800 @ 833MHz| MoBo: MSI K9A2 CF v1.0 (BIOS: 1.D)| GPU: Asus HD 6850 1024MB (DirectCu) @ 850/1100MHz | Display: L24FHD | PSU: PC Power & Cooling Silencer 750 Quad | OS: MS Windows 7 Pro x64
CPU: Pentium 4 Northwood S478 @ 3200MHz | RAM: 1,5GB DDR 400| MoBo: Gigabyte GA-8S661FXMP-RZ | GPU: ASUS Radeon X1650 Pro 256MB | Display: Dimarson 19" CRT | PSU: Noname 400W | OS: MS Windows XP Pro