Open the router via the internet and where it shows 5ghz and 2.4Ghz. Disable the 5Ghz and just use the the 2.4Ghz and see if that makes any difference.
Not using eset internet security is he as I also had problems with that.
If you give us the actual model number of the Dell we can tell if it is indeed the wireless card that is the problem.
Also another way of finding out is connect the laptop with an ethernet cable and see if it works ok using that.If so it is the wireless card that is the problem.