Mac crashes on certain/most sites

Im new here so forgive me if this isnt in the right area. At the moment im extremely annoyed, first i'm writing this on my smart phone because my Mac will not allow me to sign into any websites let alone register. I type one letter in the user name box and I vet the beach ball followed by my Mac crashing.

My Mac is outdated, but has never given me problems so I guess its the reason why iv never updated due to laziness. Im using Leopard and this all seemed to have started when I received an update from apple-something about removing flash drive because of the virus deal that was going around? But im not sure if that was what did it. I called my ISP and they told me all is well with the network so I have no idea what is going on. Id appreciate any help I can get. Sorry this is long, thanks for your time.

I would believe your ISP. A bad Internet connection wouldn't cause the beach ball but rather you'd see the progress bar in safari slow or freeze altogether.

I have a few suggestions:
First, run software update from the apple menu and install any updates.

If using Safari, try opening it but before you do anything after it opens, go to the Safari menu -> reset safari
Make sure everything is checked and click ok.

If that doesn't work, try repairing permissions on your startup disk using the disk utility.

To open Disk Utility, from the Applications folder, open Utilities, and then double-click the Disk Utility icon. In the column on the left, click your startup disk. Click the First Aid tab, and then click Repair Disk Permissions. Disk Utility will reset any files and folders with incorrect settings.