Observer not working

Question

I can't get an observer working, I'm using a fresh Magento install of 1.9.10.

My namespace: TM

My module: ProductConditions

app/etc/modules/TM_ProductConditions.xml:

<?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <TM_ProductConditions>

            <!-- Whether our module is active: true or false -->
            <active>true</active>

            <!-- Which code pool to use: core, community or local -->
            <codePool>local</codePool>

        </TM_ProductConditions>
    </modules>
</config>

app/code/local/TM/ProductConditions/etc/config.xml:

<global>
    <events>                
        <catalog_product_save_before>
            <observers>
                <ProductConditions>
                    <type>singleton</type>
                    <class>TM_ProductConditions_Model</class>
                    <method>catalog_product_save_before</method>
                </ProductConditions>
            </observers>
        </catalog_product_save_before>
    </events>
</global>

app/code/local/TM/ProductConditions/Model/Observer.php:

<?php
class TM_ProductConditions_Model_Observer
{
    public function catalog_product_save_before($observer)
    {
        file_put_contents("C:\\mage test.txt", "test");
        //$product = $observer->getProduct();
    }
}

Answer 1

This is your problem:

<class>TM_ProductConditions_Model</class>

it should be

<class>TM_ProductConditions_Model_Observer</class>

[EDIT] Your observer is not picked up because the config file is wrong.
it should look like this:

<?xml version="1.0"?>
<config>
    <modules>
        <TM_ProductConditions>
            <version>1.0.0</version>
        </TM_ProductConditions>
    </modules>
    <global>
        <events>                
            <catalog_product_save_before>
                <observers>
                    <ProductConditions>
                        <type>singleton</type>
                        <class>TM_ProductConditions_Model_Observer</class>
                        <method>catalog_product_save_before</method>
                    </ProductConditions>
                </observers>
            </catalog_product_save_before>
        </events>
    </global>
</config>   

Answer 2

You don't have a complete class reference here:

<class>TM_ProductConditions_Model</class>

It should be a full class name:

<class>TM_ProductConditions_Model_Observer</class>

You can also use the abstract factory in this node. Setup models in your config:

<config>
    <global>
        <models>
            <tm_productconditions>
                <class>Tm_ProductConditions_Model</class>
            </tm_productconditions>
        <models>
    </global>
</config>

Now you can place this in your observer:

<class>tm_productconditions/observer</class>