I did guys, I did complete reinstall of Windows 7 and now it fully activated. You're right U-Fig, I must've had some old windows update files which contributed to failed validation. I installed certificate and replaced key with one found in "Windows 7 OEM SLP Key Collection" thread on first boot to windows. I'll write the full procedure how to enable SLIC 2.1 on Probook 4720s and 4520s (same laptops, one 15", other 17") when I cool my nerves down. I would like to thank each and everyone who helped me.
Dear MeSkywalker, Can you please explain in detail how you did that, as I also bought HP 4720s and not able to Activate Win7. I am dealing with that for almost 3 days and becoming really desperate as I have tried a lot of ideas that I found on the internet, but none of them works :-( Thank you in advance.
Sorry, don't bother. I found a solution as I checked BIOS using Hex editor and it looked like that this laptop already has SLIC 2.1. So I assumed it is somehow hidden and found somewhere on this forum a utility named "HP DMI USB Boot" that creates bootable USB flash disk with some confidential HP utilities. Using that you can make SLIC 2.1 (actually SLP) become visible and voila: Win7 and Vista are automatically activated
Please give link for that " HP DMI USB Boot " utitlity . Thank you. It the same " HP USB Disk Storage Format Tool.exe " ?? Please give Proceedure . Thank you.