my wifi signal strengh get very poor why?

hi
i am using wireless internet with my laptop pc in windows 7
i use a shared connection in my appartment
and i have some problems now!:
1-i was using internet properly for months without problems
2-my wifi signal strengh was 3 at minimum and my connection speed was near 20 mbps always
but from 2-3 days ago i have some problems
like:
-my signal strengh is 1 or maximum 2 and
-my speed connection is only 2-3 mbps and sometimes even dissconnect severaly during connection
-i am not able to use the maximum speed like before with my laptop
but this problem is only belong to my laptop
i dont have same problem with my desktop pc(the only problem with desktop pc is the signal strengh)

why this happening?
how can i solve it?
note:
*the router is in same position that it was before
*i have low speed even when i am behind the router (1 feet!)
*i only have this problem with my laptop,not with my pc and phone

Oh no. It sounds like someone in the apartment might have purchased something that is interfering with your wireless signal. This can be some new wireless thing they bought, including a router. Or, a baby monitor.

So I see two choices:

Try all of the difference wireless channels available in the router's configuration utility.

Failing that, try a new router with a very different frequency band. For example, if you have a 2.4 GHz router, then try a 5 GHz router.

The funny thing is, if this is caused by a neighbor's new router, then their signal is probably all messed up too!

thanks but the problem is that i cant access to router's configuration
because i am just a user in this appartment and i don't have that password
and i don't think anyone bought a new router because in my area only 1 wireless network exist!!
and that is the one i use(so if they had a new i could see in the list)
i am sure they changed someting in the routers setting
because for few hour i didnt had internet in no any device(even my desktop pc)
after that,it was fine in my desktop pc,bt the problem begin with my laptop
but another strange problem that i have is:
i have 2 external wireless adapter and a high gain antenna (witch i use to connect with my desktop pc)
but non of them works on my laptop!!!(they work in other devices without problem)
i also disabled the internal wifi adapter and install drivers etc (and in device manager it is recognized and also said this device works properly)
but they doesn't work

so icant connect even with my external adapters
it is so strange for me...
any idea???

My best advice at this point is, talk to the person who knows the password to the router. Tell them what you're experiencing.