There is a comprehensive site dedicated to strawberries at strawberryplants.org.
They have a page dealing with this problem here:
10 Reasons Strawberry Plants Don’t Produce Strawberries
Excerpt
1. Strawberry plants are too young
Your plant is in its first year, and
still prioritising root system growth
over fruiting
2. Your strawberry plants have diseases or parasites or both
If
infected, it could be too sick to
produce strawberries.
3. Your strawberries are thirsty
Strawberries' shallow root systems
make watering tricky - make sure
there's enough
4. Your strawberries are drowning
Strawberries' shallow root systems
make watering tricky - make sure
you're not watering too much
5. Your strawberry plants are starving
Strawberries can survive on minimal
nutrients, but won't fruit
6. Your strawberry plants are high on NPK
Too much fertilizer will encourage
vigorous plant growth, but no fruit
7. Your climate is wrong for strawberries
Warm days (but not
scorching) and cool nights are optimal
for fruiting
8. Your strawberry plant variety is wrong for your climate
Strawberry
breeding programs have resulted in
varieties suitable for different
climates, check your variety
9. Your strawberry plants don’t like their home
If you're growing in
containers, take extra care with soil
and watering
10. You’ve been duped, lied to, or are misinformed
Have you been sold a
June-bearing variety when you wanted
an everbearing variety?