System lockup when downloading/transferring files

I am really hoping someone can help me here, I have spent hours trying to get help with this and have gotten nowhere.

I have an Inspiron 530 PC and I use a wireless internet connection by using a USB wireless network adapter, which functions just fine. However, if I attempt to download a file at a high speed, after 2-3 minutes of downloading either Windows Vista will completely freeze, or the USB device will somehow become disabled.

At first I thought it was the wireless network adapter, so I bought a new one. The new one has the same problem. I then tried both wireless network adapters on a different computer, and there was no problem at all. So the problem is confined to my computer.

I noticed that despite the fact that all my USB devices function, this problem occurs only when transferring files at a high speed. I then tried using a USB external hard drive to transfer files onto this computer. After 2-3 minutes, the USB device became disabled.

I also tried moving the computer and using a standard wired internet connection. I was able to download files with no problem.

In summary, the problem is isolated to my PC, as all of these devices work perfectly elsewhere. The problem ONLY occurs when transferring large files at a fast speed via the USB port. I have also tried using various different USB ports on the front or back of the PC and all of them have the same problem.

Does anyone have any suggestions on how to proceed? It appears to be a physical hardware problem with the ports, or possibly the motherboard (I hope not).

One big problem in getting this solved is that Dell's technical support people are literally incapable of understanding the problem. I have nothing personal against the Indian tech workers, but no matter what I do I am unable to get them to understand what I am saying.

After spending 20 minutes on the phone with one person, he still thought I was trying to download a file directly to an external drive by plugging the wireless adapter into it somehow. Another person told me that I need to buy more RAM, and that 2GB isn't enough to download files from the internet. They all want to use that program that takes control of your computer, in order to check for antivirus problems or increase virtual memory or mess with other settings like that. 

I have a degree in IT and work as a database manager, and am a knowledgeable computer user. Naturally I can understand why Dell treats most of their callers as inexperienced users - because it is normally true. But I know for a fact that there are no virtual memory settings that can fix this, and no computer virus preventing things from working. I believe I may need some hardware replaced. But I just can't get a Dell employee to help me.