[Help] Samsung LN40A500T1FXZA keep switching channels?!

Hi,
I have bought this Samsung LCD LN40A500 about 1.5 years. After warranty, it has a lot of problems:
- Three months ago, it sometimes switches sources between AV<->TV<->HDMI
- Two months ago, it mostly increases/decreases volume from 0-->100 or 100-->0
- And now, it keeps switching channels. ( cannot see anything)

So do you know what's the problems?

Thank you so much

Any help?

Should I replace the MAIN BOARD BN97-02715A BN41-00975C or LCD CONTROLLER V400H1-C03?

Thank you,