Start by installing the Dell Wireless 4350 control utility that came with your AP, then use that utility to search for your AP on the same local LAN. You can find that utility on the CD that came with your AP or download it from Dell's tech support pages (hint: search the tech support site for "wireless 4350").
If that doesn't work, you could try listening to the LAN with an open source LAN analyzer like Ethereal to see if the AP is generating any traffic containing its own IP address. Just configure Ethereal to filter on your AP's MAC address, which should appear on a label affixed to the bottom of your AP. Capture traffic during both AP power-up and active phases.
If the AP remains silent, you can try brute-forcing the AP's IP address using a port scanner like Nmap. This may take awhile, depending upon the address assigned to your AP. I would start by scanning 192.168.2.x, then 192.168.x.x, then the other private class B then A subnets, looking for a ping response or port 80 response (note that AP's default IP address is 192.168.2.2.).
If all else fails, reset the AP to factory defaults -- but first do your best to rebuild the filter table by using a WLAN analyzer to capture traffic sent through the AP to your LAN. Any WLAN analyzer (including Ethereal on *NIX) can track unique MAC addresses to help you determine those currently permitted to associate with your AP. Watch traffic for a few days, or until no new MAC addresses are being detected. That will at least give you a good head-start on reconfiguring the AP after you reset it back to factory default.
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