I bought TP-LINK TL-WA901ND and install it at the office. the problem is the ap usually down, and i have to unplug and plug it to connect to internet.

here is the webpage from TP Link to instaLL SOFTWARE
Download for TL WN822N V3

Manual
http://www.tp-link.com/resources/software/200912243240113.pdf

If you are using this with POE, there have been complaints that Ethernet links over 15 metres or poor cable quality can cause this effect.
Also there are warnings in the manual about keeping it clear of electrical RF interference which may also cause this effect.

Make sure that the cable is not plugged into the uplink on the router. That it is plugged in to a numbered port.

select third video - trouble shooting for the wireless adapter USB
http://www.tp-link.com.au/download/TL-WN722N_V2.html

Have you set the TP Link TL-WA901ND IP to have 192.168.1.1 as the default gateway ?
Also DHCP server is where ?
IN the TP LINK TL-WA901ND or in DLINK DIR 615
Only have one Router running DHCP and set the default gateway in the leases as 192.168.1.1.
What subnet mask are you using is it the same through out all devices ?

Use the Factory Default Reset button: First, turn off the AP's power. Second, press and hold the default Reset button then turn on the AP's power, until the system LED lights up (about 3 seconds). Last, release the reset button and wait for the AP to reboot.


Reset the factory defaults.


Here is your user manual:
http://www.tp-link.com/english/soft/20091515618.pdf


Default username and password is admin for both

Dear Joeri_troch This is Howard from TP-LINK Support Force. Could you please check if your desktop has recognized the wireless adapter? And can you see Wireless Network Connection icon?
TP-LINK Support Force http://www.tp-link.com/en/support/ http://www.facebook.com/TPLINK

you can get the manuals of how to configure tp-link tl-wa730re..just go to google and type free tp-link tl-wa730re manuals.

Log in to router via browser at: 192.168.1.1
At login and password promt enter
login: admin
password: admin

Navigate from left pane: Advanced setup -> LAN
Enter there you'r new ip: 192.168.2.1
Subnet mask: 255.255.255.0

Save

Dear,
I think this will help you http://www.tp-link.com/support/showfaq.asp?id=151