Network / Sharing :: Sony Vaio F15A1C5E - Limited Connection

I'm having problems with my sony vaio connecting to the internet. For one thing it doesn't pick up wireless signal as far away as the other laptops in the house. The main problem though, is that often the bars will be lit up as if it is connected but there will be a little yellow warning triangle saying limited.

When it happens, I try disconnecting/reconnecting and turning the router on and off but most of the time I just have to wait until it comes back. Once it is connected it works fine. It is fairly a fairly common occurrence and happens every day.

We have an Eircom router and the wireless card (according to the outside of the box) is: Wireless LAN (IEEE 802.11bgn).