Region : Greece

Model : TL-WA730RE

Hardware Version : V2

Firmware Version : 3.12.3 Build 100921 Rel.51406n

ISP : OTEnet

Hello to the community!
I usually don't make accounts and ask for other people to help me solve my problems but this time I've been searching for almost a week and still nothing.

Recently I bought the RE AP to replace my old LevelOne WAP-3000.
In my home network there is 1 desktop pc, 1 desktop server, two laptops and one android phone. The desktop pc and the server connect through ethernet cables. The other devices connect wirelessly.
The problem is with one of the two laptops. While all other wireless devices connect without problems, one laptop connects to the AP but not the gateway, so I don't have internet or access to other devices. The laptop can connect normally while in windows Vista but not in XP (it's dual boot). The other XP laptop with the same config connects normally.

I have tried both dynamic and static IP on the laptop, problem remains.
I have tried AP and extender mode (bridge with my old AP), same problem except gateway works, but only with the laptop connected with the RE via ethernet cable.
Tried both old and new firmware on the AP, same thing.
Tried several settings such as 0.0.0.0 gateway, different channel, lower tx rate, b, g, n only mode, region change, dynamic IP etc. Same problem.
I use WPA2/AES encryption, haven't tried WEP or unsecured network, don't think there is a point since the said laptop worked normally with my old LevelOne AP.
QSS on the RE cannot be disabled in any way (button greyed out). Tried connecting with TP-LINK QSS program, connected succesfully, still no gateway.

DHCP server is running on my router (LevelOne FBR-1461A), not the AP.
Router IP 192.168.1.254
AP IP 192.168.1.252
clients IP 192.168.1.110 to 250
Subnet 255.255.255.0

Any help would be appreciated. Thanks!