First of all, your computer is too old to rock'n'roll. I would suggest to uninstall all unnecessary programs as well as to check the programs being run on startup. You can use either stock msconfig or 3rd party product called Codestuff Starter that will show you more detailed view of the current configuration.

Last but not least - check the drivers as well, especially chipset and graphic card, are those installed properly?

P.S.: You czech is almost incomprehensible, so I have tried language you claim to understand and speak well.