Windows 7 - Missing Sound Video & Game Controller in Device Manager, no sound

Hi
Its bit complicated.
I have 5 year old Compaq Pressario V3611AU notebook with AMD Atholon X2 TK-55 processor. Was using Windows XP and everything working fine. Recently I upgraded RAM to 2GB & processor was changed to AMD Turion(tm) X2 TL-60 2.00Ghz. I installed windows 7 and everything worked fine for a week with no issues.
Recently when switched on it showed red cross on volume device. When I checked in device manager the sound video & Game controller has disappeared.

I checked most of the site but unable to install the exact driver.

Even I tried to add with Legacy Drivers in Device Manager but failed to install the correct driver.Even I re installed my Windows 7 but same issue. When I click on Volume device to fix the issue end up with Hardware Changes has been effected.

Please help me whether it is an issue with Sound Card or with driver.

Just download Realtek High Definition Audio Codec (Windows Vista / Windows 7 32-bit) - Reviews and free Realtek High Definition Audio Codec (Windows Vista / Windows 7 32-bit) downloads at CNET Download.com I hope its help..