Error message when starting my PC
 

Since some time when i start my PC (HP Pavillion Windows XP HOME) I get an error message in +/- 50% of the time. The error is 0x7c910c27 or 0x7c911639. Apparently it has something to do with my 2 external disc drives connected to my PC depending on when i close the electrical power of the drives or when i swith them on before or after i swith-on the PC.If anybody knows how this can be avoided , pls let me know. When i click OK when the error is schown , the PC continous running apparenly without any problem.