I've been hitting the dummy for hours but I couldn't receive a single stat...
The stats aren't locked but somehow i don't gain neither dex or str...
Go to Insula and attack the training elementals.
im pretty sure you need to be gaining in skill to get stat gains.. Are you using a skill that is already gmd? try another skill that isnt at 100 yet. Also make sure you havent reached your stat cap already.
combat skills for strength
any casting and tracking i think for int
snooping for dex
Hope that helps
You don't need to be gaining skill. What attribute are you trying to raise?
Here's the easiest ways I've found to raise stats.
Arms Lore: I think raises all 3
Evaluating Int: Intelligence
Snooping: Dexterity
Hitting Stuff or Mining: Strength
...And obvious question-- Are you sure you're not at the stat cap?
Training Dummys are only good until your skill reaches mid 30's. Training elementals will take you all the way to/past gm skill.