Const TH32CS_SNAPPROCESS As Long =  2 &
Const MAX_PATH As Integer =  260 
Private Type PROCESSENTRY32
dwSize As Long
cntUsage As Long
th32ProcessID As Long
th32DefaultHeapID As Long
th32ModuleID As Long
cntThreads As Long
th32ParentProcessID As Long
pcPriClassBase As Long
dwFlags As Long
szExeFile As String * MAX_PATH
End Type
Private Declare Function CreateToolhelpSnapshot Lib "Kernel32" Alias "CreateToolhelp32Snapshot" (ByVal lFlags As Long, ByVal lProcessID As Long) As Long
Private Declare Function ProcessFirst Lib "Kernel32" Alias "Process32First" (ByVal hSnapShot As Long, uProcess As PROCESSENTRY32) As Long
Private Declare Function ProcessNext Lib "Kernel32" Alias "Process32Next" (ByVal hSnapShot As Long, uProcess As PROCESSENTRY32) As Long
Private Declare Sub CloseHandle Lib "Kernel32" (ByVal hPass As Long)

Private Sub Command1_Click()
List1.Clear
Dim hSnapShot As Long
Dim uProcess As PROCESSENTRY32
Dim r As Long
Dim xID As Integer
Dim tt2 As String
hSnapShot = CreateToolhelpSnapshot(TH32CS_SNAPPROCESS,  0 &)
If hSnapShot =  0  Then
Exit Sub
End If
uProcess.dwSize = Len(uProcess)
r = ProcessFirst(hSnapShot, uProcess)
Do While r
List1.AddItem uProcess.szExeFile
r = ProcessNext(hSnapShot, uProcess)
tt2 = Mid(uProcess.szExeFile,  1 , InStr( 1 , uProcess.szExeFile, ".") +  3 )

If tt2 = "calc.exe" Then
MsgBox "Калькулятор уже запущен"
Exit Sub
End If
Loop
xID = Shell("C:\Windows\System32\Calc.exe",  1 )
Call CloseHandle(hSnapShot)
End Sub