Win8 running slow

Lately my laptop with Win8, has been running really slow at different times of the day. I'll get panels that say I'm not connected to the network, yet when I look at the connections it says I am connected. I called my ISP, AT&T, and they say it's the laptop. I call Dell and they tell me it's AT&T. I've run CCleaner and AVG and found nothing so I'm assuming there's no virus. When these slowdowns occur is there some way of telling just exactly who/what is causing the problem so I can go back to either Dell or AT&T and explain it to them?

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 8, 64 bit
Processor: Intel(R) Core(TM) i3-3227U CPU @ 1.90GHz, Intel64 Family 6 Model 58 Stepping 9
Processor Count: 4
RAM: 3965 Mb
Graphics Card: Intel(R) HD Graphics 4000, 1790 Mb
Hard Drives: C: Total - 462482 MB, Free - 404414 MB;
Motherboard: Dell Inc., 07PX56
Antivirus: AVG AntiVirus Free Edition 2014, Updated and Enabled