Wifi connection goes down after 30min

And a repair doesnt fix either

Power management software. Disable all of it and see if the problem goes away. Then only re-enable what's necessary.

Bear in mind you have to check the card's own power management options in addition to those for the laptop itself (screen saver, vendor power tools, etc).

That might not be a card failure. It could be some kind of authentication problem at the router. Did you try the laptop and card with other access points to be sure?

The politically and ecologically correct term is "recycle".

The bloatware might be useful for diagnosing this problem.

Are you using WPA encryption? A failed key renewal period of 1800 seconds would cause the problem. However, the common default is 3600 so that might not be the cause. There's also various power saver settings, that kill the power to the card in power save. Some cards don't recover very gracefully.

Well, if you suspect there's something broken in the XP IP network stack, you can reset it back to defaults with:

That's possible if you've been furiously adding and deleting network hardware. However, the reset will clobber any shims, add-ons, monitor programs, and LSP (layered service provider) programs that you've installed. It's a big hammer fix and I suggest you make a recoverable backup of your registry (i.e. Windoze System Restore or ERUNT) before blundering onward. If it does nothing, restore the backup.

My best guess is a power saver issue.