I think you may also check your PC power supply, sometimes, the Power supply became unstable due to life time. I don't know what's the model of your power supply. usually, you have to consider your power supply after any upgrade your pc hardware. I just have a quick look on your post, you should got two pc, right? using the power supply of stable one to run the other.

yes, you are right. and i always concern about the power of chips of USB vs the power of chips of Ethernet. Usually i believe ethernet can provide more reliable and less resource comsuming.

i know some of modules can convert the LAN to Serial Port. It also comes with a Java and C lib, for web application, i chose the java. for your case, maybe you can try the processor work with such kind of modules. it can save you alot of time by using the java lib.

if using the ActiveX. Does it makes the brower to warn the web user?