Failing to sniff ARP broadcasts

[NTWired]

Hello everyone, i'm new and just bought Wireless 802.11n USB Adapter: TP-Link TL-WN821N (300Mbps) for studying aircrack and WEP cracking.

I've installed it and got it to work with madwifi,
started a monitor mode interface and managed to run all the tests OK.
But when i start the airodump and then go with aireplay and try to catch ARP requests, im recieving none.

Now i know there are ARP broadcasts(this is my network with DLINK router) and i have my PC connected to it wirelessly + 2 roomies so there HAS to be something wrong with my actions.

Will really appriciate your help,

P.S - this is the manual i worked with:

simple_wep_crack [Aircrack-ng]
Done everything as instructed.

[Nocdem]

can u type how u did the arp replay attack , are u using a your mac ? or a clients mac to replay etc. some more info will be awsome