Wifi has limited access

DESK TOP PC Specification

Board – Asus P5G41T-M LX, serial number MT 7019017000895
Processor - 3.07 ghz Intel Pentium Dual Core
Memory – 4 gb DDR3
HDD – Hitachi 1 terrabyte
Asus TA 21 series case
OS – Win 7 Home Pro
BT Broadband up to 6Mbps

Replaced my mobo 9 months ago but did not set up the Ethernet as I had an Edimax Usb wifi connector which has consistently given me a download speed of 4.5 to 4.7 Mbps until 3 weeks ago when it dropped to 0.64 to 0.78 Mbps.
I moved the router closer to the PC and changed the filter which made no difference. I checked my 2 laptops in different parts of the house and consistently received download speeds of over 4.5 Mbps.
I followed the recent Computer Active Magazine list trying many suggestions which improved the start up time but not the download speeds.
I set up the Lan (Atheros) downloading the drivers from the Asus set up disk and immediately achieved 4.7 – 4.8 Mbps and let the PC update Win 7.
The following day after the Win 7 update the DL speed had dropped to 0.4 to 0.7 Mbps.
I checked device manager and neither Atheros Lan or Edimax USB WiFi connection had a yellow question mark to indicate a problem or in the control panel network check and there were no “unconnected cables” showing.
I have now downloaded and installed the latest drivers (Atheros comms inc (R) AR81family fast Ethernet driver from the Asus website and Atheros with no improvement.
I have removed and re-installed the drivers - no improvement.
I have followed the Asus trouble shooting procedure from their website (MAC address, IP configuration, unplugging and reconnecting the network cables – no improvement. I have followed the Windows network adapter checks enabling and resetting adapters, driver update check, disabling & re-enabling the network adapters.
When trying to connect again I received a Wan miniport error 651.
Correct user name and password inserted and again error 651 received.
Went to internet options/connections tab, selected “never dial a connection “– error 651 again
Web browser, - windows reference.com /wp, dame results-content/uploads/2009/05/raspppoe.zip, downloaded raspppoe.sys , saved to c drive
Went to Start/computer, c:\windows\system32\drivers and deleted the raspppoe sys file. Extracted new file, disabled A/Virus & firewall– same error 651.
NIC check – no conflicting devices shown
PC and router moved adjacent to ISP master plug. Switched off Lan to use WiFi pci card only. Checked download speeds still 0.62 Mbps
Re-eabled Lan and suspended WiFi - same results.
Replaced Edimax USB WiFi with a TP Link 300 Mbps Wireless N PCI Adapter card - with no improvement. Further search engine checks suggested that Win 7 driver options were not up to date.
Downloaded the Atheros driver zip file from the ASUS website, uninstalled to existing drivers & installed new ones – no improvement.

Relocated and set up my PC in a different location with different router, same ISP.
BIOS check prior to updating BIOS –
ROM type EON 25p/f80, version 0902, Date 07/272011
BIOS Image Info –
File name P5G41T-M-LX-Asus-1101, Rom, Model P5G41T-M-LX, version 1101, 06/08/2012, 18.22
Checked the download and upload speeds – no change.
Reconnected & checked the other PC from the second location, download speed of 6.9 Mbps achieved confirming a problem in my PC.
Reconnected my PC to home ISP.
Updated BIOS using Asus built in system
Went into BIOS, disabled the onboard LAN and Atheros cable.
Rechecked download speeds – no improvement.
Win 7 trouble shooting indicated wireless network adapter problem – auto fixed, no improvement.
Inssider check on channels confirmed all local WiFi set ups were using same channel (6), changed to channel 11 – no improvement
I have now run out of ideas & as internet searches suggest the problem may be with Win 7 I am looking for alternative suggestions before I fit a PCI Ethernet card.
Thanks