Hi SFDC, I'm new in the Apex world :)
I have some trouble with picklist value, i will explain.
I have a picklist that show me the StartDate from the Period Objects.
I have also a List of ForecastingQuota by User.
The problem is that when I select a value in the picklist, the controller doesn't get it, so my query wich show the user can't change.
Controller :

public List<SelectOption> optionspl {get;set;}
public List<User> resultsusers{get;set;}
public Date dateinput{get;set;}
public Date dateinput2 {get;set;}


public List<SelectOption> getPeriodList(){
 		List<SelectOption> optionspl = new List<SelectOption>();
 		List<SObject> resultspl = [SELECT FullyQualifiedLabel, StartDate FROM Period WHERE StartDate > TODAY AND Type = 'Quarter'];
 		for(SObject pl : resultspl){
 			optionspl.add(new SelectOption(String.valueOf(pl.get('StartDate')),String.valueOf(pl.get('StartDate'))));
 		}
 		return optionspl;
 	}

public  List<ForecastingQuota> getAllQuotas(){
		dateinput = Date.today();
		date mydate2 = mydate.addDays(90);

		List<ForecastingQuota> resultsquotas = new List<ForecastingQuota>();
	    resultsquotas = [SELECT Id,QuotaAmount,QuotaOwnerId, StartDate FROM ForecastingQuota WHERE StartDate >:dateinput AND StartDate <:mydate2 ORDER BY QuotaOwnerId, StartDate ASC];
	    
	    List<User> resultsusers = new List<User>();
		resultsusers = [SELECT Id FROM User WHERE IsActive = TRUE AND ForecastEnabled = TRUE LIMIT 999];

		Map<Id, ForecastingQuota> fqsByOwnerId = new Map<Id, ForecastingQuota>();
			for (ForecastingQuota fq : resultsquotas)
			{
			    fqsByOwnerId.put(fq.QuotaOwnerId, fq);
			}
		
			// new map of quotas keyed by all user ids
		Map<Id, ForecastingQuota> allUserFqsByOwnerId = new Map<Id, ForecastingQuota>();
			for (User u : resultsusers)
			{
			     allUserFqsByOwnerId.put(u.id, fqsByOwnerId.containsKey(u.id) ? fqsByOwnerId.get(u.id) : new ForecastingQuota(QuotaOwnerId = u.id, QuotaAmount = null));
			    	
			}
			List<ForecastingQuota> allthequotas = new List<ForecastingQuota>();
			allthequotas = allUserFqsByOwnerId.values();
			allthequotas.sort();
			return allthequotas;
	}

And the VFP code :

<apex:pageBlockSection columns="4">
<apex:selectList value="{!dateinput2}" id="dateinput2" size="1">
    <apex:selectOptions value="{!periodlist}" />
     <apex:actionSupport event="onchange" rerender="allquotas"/>
</apex:selectList>
			<apex:pageBlockTable value="{!allquotas}" var="key">
				<apex:column>
				<input type="checkbox" name="pouet"/>
				</apex:column>
				<apex:column headerValue="Name">
				    <apex:outputField  value="{!key.QuotaOwnerId}"/>
				</apex:column>
    			<apex:column headerValue="Quota">
			    	<apex:inputField value="{!key.QuotaAmount}"/>
			    </apex:column>
			    <apex:column headerValue="Date">
			    	<apex:outputField value="{!key.StartDate}"/>
			    </apex:column>
			</apex:pageBlockTable>
</apex:pageBlockSection>
</apex:pageBlock>

Thank's for the help :)