wifi adaptor not recognized, usb wifi hogging wifi resources

recently i was having major computer issues on my desktop, i did a full restore to factory settings and after doing a few windows updates i found that my network adaptor was not finding any signals. it does not show up in the change adaptor settings page or in the device manager page. when i troubleshoot my internet connection it says an ethernet cable is not properly plugged in. I have a desktop computer but it definately has a wireless network card. i used to get windows updates for it and it just stopped working one day. when i look in the BIOS the only option related to booting a network card is B03 D00 Yukon PXE. no matter when i boot it i still dont get wireless signals. when i go into the boot menu and try to boot this device it says " PXE E61: media test failure please check cable" i have opened the tower and the card is securely in its slot. i thought i would workaround by getting a usb wifi card. I installed it and connected to the internet and it alternated between having a connection to the internet and being connected to the network but not the internet. even when it is connected to the internet i cannot reach any web pages. my dropbox desktop files update very slowly (7kb/s). when i am connected with the usb card the network stops working for everyone else in the house. they can no longer reach web pages or continue downloads. please help.

gateway DX4300
AMD Phenom II X4 810 processor 2.60 GHz
8.00 GB DDRII RAM
windows 7 home premium

EDIT: additionally nothing shows up when i scan with avast antivirus