A problem has been detcted and windows had been

Simply enough, try going to system restore in the control panel under "Performance and Maintenance" then on the "System" choice look to your left top. there will be System restore unless you've changed to classic view, then you'll have to look at all the icons till you find it. Go back to the nearest day(in bold print) before this started and you should be all set.

This is a windows stop error. Are you running windows XP?

If it is the first time you have seen it you can try restarting and it may never appear again. If it does:

At the bottom of the screen you will see some text saying STOP ERROR: 0x000000?? (0x???????? 0x???????? 0x???????? 0x????????)

Look at the code prior to the brackets 0x000000?? - write it down and google "STOP ERROR 0x000000??".

This will let you know what is causing the STOP error. Very common reasons for this are component reseating required and disk-checking. You can run a diskcheck through the Windows Recovery Console (can be installed to hard-disk - simplest way is to install combofix and follow the onscreen instructions - or run from your windows installation disc).