I've just bought PMDG 737.
Can you please tell me if there are any known problems with this software, before I load it.
Not anymore. The PMDG 737NG is (by now) quite an old add-on and has had numerous updates and patches. Make sure you have all of them and your system is compatible. Some people say it eats up a lot of resources, lowering frame rate, but other than that it should work fine.
Thanks Bindolaf for your help
mine dosen't eat a lot of frames, but maybe thats cuz i always do the 2-D cockpit