Cannot connect wirelessly to network

Yesterday I lost internet connection, so after resetting my wireless router, I tried to set up a new wireless network and connect. However, when I connected my laptop to the router via a hardwire, Network and Sharing Centre said that there was no network access and no internet access. After phoning my IPS today, and setting up a new wireless network, I am able to connect to my network and to the internet via hardwire, but when I unplug the cable, I remain connected to my network, but I get the same message in the Network and Sharing Centre as I did before, no network access and no internet access.

After phoning my IPS about it, they advised me to contact Dell, as it seems that my laptop is trying to use previously saved settings to connect to the new wireless network. In properties I have changed the security settings to match the network's security settings, but I still cannot wirelessly connect. Dell said that they could remotely access my laptop and attempt to fix the issue for a fee, but as I'm a student and a bit low on funds, I would like to avoid said fee. Is there anything I can do myself to fix this issue?

The laptop is an Inspiron 1545 running Windows 7 64-bit, and the wireless router is a D-Link (model unknown).

Additionally, I have a desktop that can connect to the wireless network without any issue, so I think the problem is isolated to the laptop.

(I'll add screenshots if needed, I need more posts to do so though.)

Thanks in advance.
 
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