Lan card auto disconnect & connect.

Hello everyone,
i am facing the problem of lan card auto disconnect & connect.I have an assembled pc dual core with realtek lan card.Some days before everything was ok.But from 2 days this problem occurred.I googled related to this & found nothing working. Please help...
i am using tenda router & connected 4 others computers also which working fine on this lan cable.Unistalled lan driver installed new from rtl site.
disabled energy efficient ethernet.
disabled shutdown -wake on lan.
reset winsock
reset ipv4
reset ipv6

When you say disconnecting, does it change to red cross or yellow no internet connection (limited)?

All PCs have dynamic IPs? Any other DHCP server running in the network?

Try a System Restore to a date prior to the issue - System Restore
Is that 2nd DNS server (202.56.230.2) working? Run in cmd:

Code:

nslookup
server 202.56.230.2
google.com

Does it respond back with the IP addresses?
If not remove it.

its went yellow first & than shows unplugged,sometime in network connection there is no connection of lan card.
I formatted the windows 7 installed a new 1 & checked, found same problem, than i installed win XP & the problem is still there
right now i am using win 7 *64 & no solution.
there is no another DHCP , When i ping to any IP even router IP address its HOST UNREACHABLE.

If it is still same with both Win 7 and XP, either router needs a factory reset or ethernet card is malfunctioning. Try factory reset (check router manual).

Tried factory reset. No solution......On this cable & router its working fine on another computer....

Try changing MAC Address of the network card with Win7 MAC Address Changer v2.0
Take note of original and then change last 2 fields.