Hardware

There are a couple of reasons of this:

Your Internet Connection is damaged

If you used to play this game without issues, then it may be that your internet connection has been damaged, due to time or other circumstances. This is how to repair it:

1. Go to your Windows start menu.

2. Go under Help and Support.

3. When the window pops up (it may take a second or two), type in the searchbox in the upper-right corner Repair Connection.

4. A new page on the window should come up. in the left box area, click the first topic, stating Repair a LAN or high-speed Internet connection.

5. Follow the instructions given in the right area of window.

Your PC may be slow

If this problem has been here since you started playing, then it may be that your pc is slow. Here's a couple of tips to help this out:

1. You could run the Disk Defragmenter, which has been known to help your pc run faster for it organizing all your files.

2. Your pc may just be slow because of it's low memory. Try uninstalling a few programs to help it out.

3. This may be the most powerful tip of all. Buy more memory for your pc. Roblox runs decently at around 256MB, recommended at 512MB or more. To see what your pc's memory amount is, go to the Control Panel, then to Performance and Mantainance, then to the System Icon, normally located as the bottom-right icon. The window that comes up should show how much MB your pc has.