|1- You cannot have McAfee and Avast installed at the same time, there is a conflict. Uninstall McAfee and you machine will run much better overall.|
2- See if there are drivers available for your 'plug and play broadband' device on the mfg's website, if there are, it will definitely help.
3- Run Memtest86 from a bootable CD to test your memory, you may also have a memory segment error/problem. Repeat the test with one stick of memory at a time if you get any errors. Replace as needed.
4- Install Speedfan or other temperature monitoring program to see if you are overheating. If you are, then you probably need to clean out your laptop's vents of accumulated dust (use compressed air can into all vents and access panels).
Post back results.
You have to be a little bit crazy to keep you from going insane.