Realtek audio driver problem

Hello,
Since I bought the DZ77SL-50k intel motherboard I have a problem with the realtek audio driver.Sometimes after restarts it will disappear from device manager but I can still see it in Control Panel uninstall a program.I installed windows several times and still get this problem.Right now I have no sound (it shows no speakers or headphones are plugged in ) and I have the default windows sound driver that is not working.I don't know why but if I shut down the computer and leave it closed for several hours the driver may work again.
Can it be hardware related? If so will buying an external sound card solve my problem? I'm getting really tired of this issue.
I have windows 7 64 bits

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 7 Professional, Service Pack 1, 64 bit
Processor: Intel(R) Core(TM) i5-3570 CPU @ 3.40GHz, Intel64 Family 6 Model 58 Stepping 9
Processor Count: 4
RAM: 8157 Mb
Graphics Card: NVIDIA GeForce GTX 660, -2048 Mb
Hard Drives: C: Total - 599517 MB, Free - 523079 MB; D: Total - 353798 MB, Free - 255860 MB;
Motherboard: Intel Corporation, DZ77SL-50K
Antivirus: Avira Antivirus, Updated and Enabled