If is a driver issue updating the drivers normally solves that, if a signal or channel interference issue that can be remedied.

After updating the drivers i would not expect the wireless card ot disappear from device manager so it possibly points to hardware. You could check that the physical card is seated correctly if in a desktop or if in laptop again that it has not come loose and all the antannae are connected and secure.

After that has been done and the issue is still appearing i would open a cmd prompt by right clicking and choosing to run as administrator and type:

sfc /scannow press enter

Let it repair anything it finds and restart computer if prompted to do so.

Also from a cmd prompt do a chkdsk /r

If no change from the above please backup all your important files and data.

Then please do a clean install to eliminate any software issues.

Link below for a branded computer clean install if you have have no recovery partition or recovery discs to recover the system to factory defaults.

Clean Reinstall - Factory OEM Windows 7[2]=General%20Tips

If you have a custom built computer with no means of recovery excpt for the MS Windows 7 Operating system disc.

Clean Install Windows 7[2]=General%20Tips