Win Vista PC wont connect to the net

Hello,
We bought a NEW Windows Vista Desktop PC in June 2008 from the Base Exchange, for the reason that my son wanted to play some online games a Windows XP slow speed could not run. We really enjoyed the wonders of it, until it went bananas last December, 2009. For some bizarre reason, it KICKED ITSELF OFF the net connection and won't come back on. This happened in an accelerated frequency. We performed the usual tasks of: dis- and re-connected cables (from and back to a router and a wireless, checked cable functionality etc.), rebooted etc..The HP diagnose and repair suggestions didn't help at all. One thought that the NIC card maybe failing, and so a NEW one had been put in. No luck on this one. Another thought came to our minds that maybe restoring the op system will solve it (due to virus had penetrated into the OP System restore and jamming things up). Still no luck! The HP via phone had been consulted and we requested for a FULL RECOVERY disc. Loaded them 2x in separate occasions due to this existent problem still unresolved. We are running out of patience, so to speak. We have another but old Windows XP Desktop PC running ok and a Compaq notebook, also running ok (via wireless). We appreciate any help on this adamant Windows Vista that is a paper weight ATM :-(