Fix Wordpress blog performance problems

Hi, I need a wordpress **specialist** (you have already experience is fixing plugins, slow installations by tweaking advanced wordpress configuration parameters) and webmster (you are able to check how much you actually speed up the website), to look at my website (a Wordpress with standard themes on a dedicated server), and help me solve the following problem - a few days ago the loading of pages took under 1 second - after a few plugin install / changes, it now takes **minutes** to display. **Your mission is to lower the loading time to under a second again.** More projects may come for the successful worker. Thanks in advance for your bids !!!!