Linked list problem

I'm having a little problem with my linked list. What am I doing wrong?

Here's the source

Code:

#include <string>
#include <iostream>
using namespace std;

class Inventory
{
private:
	typedef struct node
	{
		struct node* next;
		string value;
	};
	node *head;
public:
	Inventory()
	{
		head=NULL;
	}
	void PickUp(string item)
	{
		node* newNode, *nodeMove, *previousNode;
		newNode = new node;
		newNode->value = item;
		if(!head)
		{
			newNode = head;
			newNode->next = NULL; //the debugger says this is the line that messes up.
		}
		else
		{
			nodeMove = head;
		    while (nodeMove != NULL && nodeMove->value < item) 
			{
			    previousNode = nodeMove; 
				nodeMove = nodeMove->next; 
			} 
			if (previousNode == NULL) 
			{ 
				head = newNode; 
				newNode->next = nodeMove; 
			} 
			else 
			{ 
				previousNode->next = newNode; 
				newNode->next = nodeMove; 
			}
		}
	}
	void DisplayInv()
	{
		node *nodeMove; 
		nodeMove = head; 
		while (nodeMove) 
		{ 
			cout << nodeMove->value << endl; 
			nodeMove = nodeMove->next; 
		}
	}
	~Inventory() 
	{ 
		node *nodeMove, *nextNode; 
		nodeMove = head; 
		while (nodeMove != NULL) 
		{ 
			nextNode = nodeMove->next; 
			delete nodeMove; 
			nodeMove = nextNode; 
		} 
	} 

};

void main() 
{
	int choice = 0;
	string Value;
	Inventory List;
	cout << "Test v1.0" << endl;
	cout << "1. Add item." << endl;
	cout << "2. Exit." << endl;
	cin >> choice;
	switch(choice)
	{
	case 1: cout << "Type in the item you want to pick up." << endl;
		cin >> Value;
		List.PickUp(Value);
		List.DisplayInv();
		break;
	case 2: List.~Inventory();
		break;
	}
}

I get an application error that says "The memory could not be 'written' "
Thanks in advance
-Psycho

I think

Code:

if(!head)
		{
			newNode = head;
			newNode->next = NULL;
		}

should be

Code:

if(!head)
		{
			newNode->next = NULL;
                        head = newNode;
			
		}

I haven't read past this so there could be more wrong.

woo! it works, thanks

it gets annoying when I mess a little thing up like that and I spend so much time on something that's so simple.

Sorry to bug you guys again, but I'm getting an error at random times when inputting values in my linked list

ERROR:
Run-Time Check Failure #3 - The variable 'previousNode' is being used without being defined.

Code:

#include <string>
#include <iostream>
using namespace std;

class Inventory
{
private:
	typedef struct node
	{
		struct node* next;
		string value;
	};
	node *head;
public:
	Inventory()
	{
		head=NULL;
	}
	void PickUp(string item)
	{
		node* newNode, *nodeMove, *previousNode;
		newNode = new node;
		newNode->value = item;
		if(!head)
		{
			head = newNode;
			newNode->next = NULL; 
		}
		else
		{
			nodeMove = head;
		    while (nodeMove != NULL && nodeMove->value < item) 
			{
			    previousNode = nodeMove; 
				nodeMove = nodeMove->next; 
			} 
			if (previousNode == NULL) // this is the first place the debugger says the above mentioned error
			{ 
				head = newNode; 
				newNode->next = nodeMove; 
			} 
			else 
			{ 
				previousNode->next = newNode;  //heres the other place the debugger says the same error. :(
				newNode->next = nodeMove; 
			}
		}
	}
	void DisplayInv()
	{
		node *nodeMove; 
		nodeMove = head; 
		while (nodeMove) 
		{ 
			cout << nodeMove->value << endl; 
			nodeMove = nodeMove->next; 
		}
	}
	~Inventory() 
	{ 
		node *nodeMove, *nextNode; 
		nodeMove = head; 
		while (nodeMove != NULL) 
		{ 
			nextNode = nodeMove->next; 
			delete nodeMove; 
			nodeMove = nextNode; 
		} 
	} 

};

void main() 
{
	int choice = 0;
	string Value;
	Inventory List;
	cout << "Test v1.0" << endl;
	cout << "1. Add item." << endl;
	cout << "2. Exit." << endl;
	cin >> choice;
	switch(choice)
	{
	case 1: cout << "Type in the item you want to pick up." << endl;
		cin >> Value;
		List.PickUp(Value);
		List.DisplayInv();
		break;
	case 2: List.~Inventory();
		break;
	}
}

when running the program I get this error at random times. Sometimes after the user puts in 10 values sometimes when the user puts in 3 values etc. dunno, its weird and I have no clue what I'm doing wrong.