urvashijt;
Hello and welcome to the forums.
Well I guess we can rule out hardware issues since your linux distro seems to work fine.
The problem would seem to be within Win7 and I would suspect that it is a driver issue, so....
type device manager into the search box and hit enter to open device manager
expand network adapters
select then right click the problem wireless adapter and choose properties, then
select the driver tab and click the Roll Back Drive Button. Answer any subsequent prompts in the affirmative and reboot the computer.
If that doesn't help. Do it again and reboot, you may need to do this a few times until you arrive back at the driver that has actually worked in the past.
Failing that then you need to consider any third party AntiVirus / Internet Security Suites (Norton/Symantec, McAfee, AVG, etc.,) and or third party firewall such as (Comodo, ZoneAlarm, etc.,) that may be causing the issue and are unique to your Windows 7 install.
Remove any such products by using the Control Panel > Programs and Features applet and then run the vendor specific proprietary removal tool to make sure there are no remnants of the product remaining. There is a short list
Link Removed if yours is not included in the list please google for the removal tool for your product. Consider replacing any such products with the built-in Windows firewall and
Link Removed due to 404 Error.
You won't actually be able to do this from work but I've include a list of ideas for you to consider at home from one of the Dell support forums.
Update the firmware in your wireless router. Manufacturer's website, make & Model needed. (Probably the most important)
Broadcast SSID(You may want to change this to make it easier to connect)
Use WPA-PSK(TKIP) Security(WPA Personal). Most wireless devices work best with this type of security. (Also rather important)
Password at least 13 characters long.
Mixed b and g mode(n if available)(Use this mode only if using a print server and/or USB wireless adaptrer(s))
Use channels 1, 6 or 11. Most devices work better on these channels.
Keep the setting at DHCP.
Do NOT use Mac Address Filtering
Save and exit. Power everything off for 30 seconds. Power everything back on, wait 30 seconds, now try to connect.
SOURCE:
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Keep us posted.