Realtek High Definition Audio isn't working - No Audio Device installed

Well I've been dealing with this technical difficulties since awhile but through times it gets worse than before. It was started when I was still using Windows XP, one day my sound stopped working, I tried to reboot my laptop, it didn't work. Then I was suggested to upgrade my OS to a latest windows version so I upgraded my OS to Windows 7. Well the next day after I did, the sound seemed working fine but then I left my laptop unused because I had to get on a surgery for about 2 weeks. After 2 weeks, the problem reappeared. One thing that I notified is there is always a red cross mark at the sound icon on the taskbar whenever the sound stopped working and when I clicked on it, it said "No Audio Device installed". I tried to uninstall the driver (I'm using Realtek Audio ALC288_v6.0.5901 which is compatible with my current OS), and then re-install the driver but it didn't work. Well I've tried to fix it both in Safe mode and normal mode, but it didn't work either, but what's pretty confusing is, eventhough Realtek didn't work sometimes I can use the sound with High Definition Audio, which I suspected is the integrated sound card but it doesn't work all the time, it's like when I need the sound the most, it won't be there but if I'm just trying to see if it works, it will work. I don't know whether it's a problem with my current system or with the soundcard itself. I really need assistance. For details, I'm using Acer Aspire 4520 with AMD Turion 64x2 processor. Thank you very much.

Regards,

Dessi.