PyQt processing causing GUI lag

I am writing an application in Qt using python that will process a txt file. The user selects a file from their hard drive and the program will open and process it. The main problem I am having is that the 1st time you run it, it is fine; but if you run it multiple times without restarting the program, each time after the 1st will take the same exact amount of time, but the progress bar lags and sometimes the file select dialog does not go away until the processing is complete. Here is the code below. I know the indentation is wrong, it would not copy properly. Can anyone see a part that may cause the lag after the 1st run?

import sys,  time,  os
from PyQt4 import QtCore, QtGui
from PyQt4.QtCore import *
from PyQt4.QtGui import *

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    _fromUtf8 = lambda s: s

class Ui_MainWindow(QtGui.QMainWindow):

    def updateProgress(self):
        self.progressBar.setValue(self.progressBar.value()+1)
        self.progressBar.repaint()

def processCollect(self):
    filename = None
    self.progressBar.setValue(0)

    #Get the filename from user
    try:
        filename = QtGui.QFileDialog.getOpenFileName(self,  "Open Collect",  sys.path[1] + "/",  "Text files (*.txt)")
    except IOError:
        filename == None

    if filename:
        #Find number of lines
        file = open(filename,  "r")
        linecount = 0
        for line in file:
            linecount = linecount+1
        file.close()
        print(linecount)

        #Set up progress bar
        self.progressBar.setMinimum(0)
        self.progressBar.setMaximum(linecount)
        self.progressBar.show()

        #Read file contents and update progress bar
        file = open(filename,  "r")
        for line in file:
            line = line.replace("\n", "")
            print(line)
            time.sleep(.05)
            self.updateProgress()
        file.close()

def setupUi(self, MainWindow):
    #Create the main window
    MainWindow.setObjectName(_fromUtf8("MainWindow"))
    MainWindow.resize(800, 600)

    #Body of the main window
    self.centralwidget = QtGui.QWidget(MainWindow)

    #Add process collect button
    self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
    self.centralwidget.buttonProcessCollect = QtGui.QPushButton(self.centralwidget)
    self.centralwidget.buttonProcessCollect.setGeometry(QtCore.QRect(310, 240, 120, 40))
    self.centralwidget.buttonProcessCollect.setObjectName(_fromUtf8("buttonProcessCollect"))

    #Add progress bar
    self.progressBar = QtGui.QProgressBar(self.centralwidget)
    self.progressBar.setGeometry(QtCore.QRect(165, 290, 430, 20))
    self.progressBar.setProperty("value", 0)
    self.progressBar.setObjectName("progressBar")
    self.progressBar.hide()

    #Add actions to body
    self.centralwidget.connect(self.centralwidget.buttonProcessCollect,  SIGNAL("clicked()"),  self.processCollect)

    #Add body to the menu
    MainWindow.setCentralWidget(self.centralwidget)

    #Add text
    self.retranslateUi(MainWindow)

    #Connect actions
    QtCore.QMetaObject.connectSlotsByName(MainWindow)

def retranslateUi(self, MainWindow):
    MainWindow.setWindowTitle(QtGui.QApplication.translate("MainWindow", "MainWindow", None, QtGui.QApplication.UnicodeUTF8))
    self.centralwidget.buttonProcessCollect.setText(QtGui.QApplication.translate("MainWindow", "Process Collect", None, QtGui.QApplication.UnicodeUTF8))

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())