In short, handedness is the characteristic that provides a variety of biomolecules with their ability to recognize and regulate sundry biological processes. And silicon doesn't form many compounds having handedness. Thus, it would be difficult for a silicon-based life-form to achieve all of the wonderful regulating and recognition functions that carbon-based enzymes perform for us.
All the same, chemists have worked tirelessly to create new silicon compounds, ever since Frederic Stanley Kipping (1863-1949) showed that some interesting ones could be made. The highest international prize in the silicon area is called the Kipping Award. But despite years of work--and despite all the reagents available to the modern alchemist--many silicon analogs of carbon compounds just cannot be formed. Thermodynamic data confirm these analogs are often too unstable or too reactive.
It is possible to think of micro- and nano-structures of silicon; solar-powered silicon forms for energy and sight; a silicone fluid that could carry oxidants to contracting muscle-like elements made of other silicones; skeletal materials of silicates; silicone membranes; and even cavities in silicate zeolites that have handedness. Some of these structures even look alive. But the chemistries needed to create a life-form are simply not there. The complex dance of life requires interlocking chains of reactions. And these reactions can only take place within a narrow range of temperatures and pH levels. Given such constraints, carbon can and silicon can't.
There is one thing silicon can do. Life on earth is predominantly made up of right-hand carbohydrates and left-hand amino acids. Why do they not have the opposite handedness, or both have the same? Many chemists believe that the first "handed" carbon compounds formed in a "soupy" rock pool having a "handed" silica surface. And the handedness of this surface encouraged the creation of those carbon compounds now preferred in Earth's life-forms.