my venezuilan suntiger cant climb!!!!
anyone know perhaps Why?

She may be entering premoult, I noticed they loose there climbing abilities somewhat during that stage

i thaught so to but she molted 3 weaks ago and shes 8cm????
i dont know why?

With can't climb, are you referring to can't climb against ANY surface or specific surfaces?

Tarantulas might struggle to climb against glass / perspex in a brand new enclosure, they still can, but very slowly and sometimes lose their grip. Seems that they put a layer of silk where they move which helps with the stickiness of the surface over time. This is what I have observed and simply my opinion.

You should be able to see cat-like retractable claws at that size fairly easily. If you don't see them when it is climbing on wood for example, there might be something wrong. Has it done this before the molt or was it fine? Is it the same enclosure?

ive had her for three monthes, not once has she been able to climb.
when i got her she couldent, and now even she doesent.
the same cage,
glass,
claws are viseble but im worried. shes my baby. hahaha

Is she visibly struggling to climb or just not bothering to climb?
My P irminia is on the substrate 99% of the time, very rarely bothers to climb. Psalmopoeus are what is known as semi-arboreal, but are also opportunistic burrowers. So if they can make a hide on the ground, they most probably will.