wireless adapter problem

I recently purchased a linksys Compact Wireless-G USB adapter for my Vista machine as my apt. building has free wifi. I've been experiencing an intermitant problem that is occuring more and more often.
When I start the computer and Windows comes up, the Linksys driver(?) comes on, then goes off, then comes on, then off and will continue this way until I pull the adapter or shut down. If I click the icon to select a network, the available networks will show up, then disappear, show up, disappear as though I were plugging and unplugging the adapter over and over.
The only way I can end up getting online is to uninstall, then reinstall the Linksys software, shut down before plugging the adapter in, restart and then insert the adapter. This sometimes works the first time, sometimes not.
Yesterday when already connected, it started doing this again(as revealed by that annoying, 'ker-plunck' sound the Windows makes when you plug something in), and did it for a few seconds before settling down and allowing me to reload my page.
The first time this happened, I had replaced my old D-Link wireless adapter and forgot to uninstall the D-Link software first. Thinking that was the cause, I uninstalled that and re-installed the Lynksys software. That worked for awhile, but I had the same problem after the comp went into 'sleep-mode' while online. Since then it's been happening more and more often.
A couple of weeks ago my comp stopped working(wouldn't boot), so I took it to a repair shop. They replaced the hard drive, re-installed Windows Vista Home Premium and it seemed for a couple days to be fine. Certainly, the thing is quieter. But then the problem came back with a vengence. It's now an everyday occurence. Any thoughts anyone? Thanks very much in advance.