This is really a Networking Forum posting, but no worries.
Simplest thing to try for now is;
> switch off all your PCs.
> Disconnect the power to your Wireless router
> Disconnect the power to your Broadband modem
> Wait 5 minutes
> Power up your Broadband modem, & wait a few minutes for it to settle down
> Power up your Wirless router & wait a few minutes again.
> Switch on your PCs and check for wireless connection (The DELL should have released the assigned IP address and be given a new one. If not, it still will not work and we can post the next suggested actions)