Jerez, Spain - Former World champion Williams launched its new cars and declared a fresh start after enduring its worst season in Formula 1.A Renault engine has replaced the 2011 Cosworth, Bruno Senna has ousted veteran compatriot Rubens Barrichello, and a new technical line-up is in charge after the departures of Sam Michael and Patrick Head.The dark-blue-and-white FW34 that was rolled out of the garage without fanfare before the first pre-season test was without doubt the least-attractive Williams since the 'walrus-nosed' FW26 of 2004. It featured the now conventional stepped nose that has appeared on all the 2012 cars with the exception of McLaren.BACK IN THE FIGHTWilliams, which scored only five points in 2011 with Barrichello and Pastor Maldonado, will not care how it looks so long as it is quicker and more reliable than its predecessor. Team founder Frank Williams said: "One could say that looking at the Williams F1 Team today we are off to a truly fresh start."We have a new car, new drivers, new engine and new senior personnel. We also have a number of new partners who have joined the team in the past few months. The team has had a good off-season at the factory and we feel ready and strong for the fight."While the Renault engine is the same as that used by 2010/11 champion Red Bull, it is also identical to those powering Caterham, the former Team Lotus which has yet to score a point.'REALLY MOTIVATED'The roll-out was a novelty for Senna, who scored two points and started the final eight races of 2011 with Renault. He made his F1 debut in 2010 with struggling HRT, which did not have a car ready to test that year. He said: "This is my first pre-season testing programme since I started in F1 two years ago."I'm really motivated and looking forward to working hard with everyone in the team. I hope we have a successful month testing and developing the car so we arrive in Melbourne as well-prepared as possible."Melbourne will host the opening 2012 GP on March 18.