Macbook's WIFI keeps disconnecting from Thomson TG789Pvn router only

Hi community,

I have a very strange issue and I really hope someone with the expertise in WIFI to help solve my problem.

My hardware:

• 13-inch Mid 2007 White Macbook
• Thomson TG789Pvn router provided by ISP (Exchanged for the same router model, but still have the problem) for my home.

My Software:

• OS X 10.7.5
• Using DHCP to connect to router for internet

My problem is:

My wifi keeps disconnecting from the router many times in short period of time (ie 5 disconnection within 10 mins time frame, worse case probably). Sometime, it stay connected for half hour or more.

My situation:

I have my macbook and have been using the original Thomson (TG789Pvn) router for 2 years now and there wasn't any problem. The problem came to light around mid 2013.

I have exchanged a new router (same model TG789Pvn) and still the problem existed.

I can connect to other routers without any disconnection problem using my macbook (ie my office, public WIFI)

Tried some possible solution from web but without success:

• Have tried PRAM my macbook.
• Have tried Removing the SystemConfiguration folder in the Library Preferences and reenter details for the WIFI connection.
• Have tried configuring manually my IP for temporary solution. (It still keeps disconnecting BUT when I click on the WIFI for it to refresh the list, I can connect back to internet by pinging google) - I am testing using ping command on terminal)
• Have tried doing the unload killall mDNSResponder

All without success.

One strange scenario that is helping me out in staying connected for longer period of time (more than 6 hours):

When I use VPN to connect to internet via this router and my macbook, it temporary fixing my disconnection issue.

Anyone knows what is happening?

Really appreciate if anyone can solve my problem!