cannot ping win7 or access shares from XP

[OverWorked]

I have a share on my Win 7 machine. I've just tried accesing it from an XP machine and it can't find it. XP can't ping the Win7 machine either.

This has started recently. It was all working a few weeks ago. The share is for making msi packages with WinInstall. I've been using it all year no problems, today I've tried to use it to make an image and XP machines can't see the Win7 share or ping the Win7 machine.

I think some windows update may have broken it.

Previously the firewall was switched off in the domain profile. I've switched it back on and set an exception rule to allow ping - still no joy.

Any ideas? Thanks.

[OverWorked]

I've just discovered it's a DNS issue. The DNS A record for the machine is two months old. Now I need to find out why.

If I use the correct IP address, the ping and shares work OK.