Unhandled exception and Access violation for every program

I was working on some programs and now, no matter which one I run, I get an error like this: Unhandled exception at 0x00411be0 in program.exe: 0xC0000005: Access violation writing location 0x00130000.

Any ideas what is causing this or how I can fix it?

[MosaicFuneral]

Have you ran through the code till this occurred?
And actual code is nice, too.

There are specifically two of them that are giving me this problem. The error appears as a pop-up. The debug tool, however, doesn't show an error.

#include <stdio.h>
#include <string.h>
#include "string.h"
void assemble(char*input, int num, char let, float flo);

int main() 
{
	char input[255];
	int num;
	char let;
	float flo;

printf("\nPlease enter an integer:\n");
	scanf("%d", &num);
	printf("\nPlease enter a character:\n");
	scanf("%c", &let);
	printf("\nPlease enter a floating point number:\n");
	scanf("%f", &flo);

	assemble(input, num, let, flo);
	puts(input);
	return 0;
}

void assemble(char *input, int num, char let, float flo)
 {	
	sprintf(input, "%d, %c, %f", num, let, flo);	
 }

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>


int main()
{
	#define MAXCHARS 300
	void convertToUpper(char[]);
	FILE *inFile;
	char fileName[25];
	char text[MAXCHARS];

	printf("\nEnter a file name: ");
	gets(fileName);
	inFile = fopen(fileName, "r"); /*This opens the file */
	if (inFile == NULL)			   /*Checks that the file exists*/

	{
		printf("\nThe file %s was not opened successfully.", fileName);
		printf("\nPlease check that you entered the file name correctly.\n");
		exit(1);
	}
	while (fscanf(inFile, "%s", text) !=EOF) /*Reads and displays the file*/

		convertToUpper(text);
		printf("%s\n", text);
	fclose(inFile);
	return 0;
}

void convertToUpper(char text[MAXCHARS])
{
	int i;
	for(i = 0; text[i] != '0'; i++)
		text[i] = toupper(text[i]);
}

I managed to fix the first one, so now I just need help with the second program.

[MosaicFuneral]

You do not declare, or define functions in other functions.
Macros tend to go outside publicly.
Are you actually modifying text[] in convertToUpper()?
You loop and call a function, but only call printf() once, because you're missing something.
If the file didn't open, do you have to frantically escape, and not just pass over code with an if-else condition?