I can't get on from my home computer, either, but I can from my work computer. I can even log on from work. I get the impression they blocked the IP addresses of all their users, so you can't log on from the computer your account is registered to.
Still can't add any more money to my account, though... it rejects my perfectly good credit card. I've had an album sitting in my basket since May. HDGiants has a Facebook account, and I tried posting a polite message to the effect of, "Are you ever coming back?" and IT WAS DELETED. I also PM'd their CEO Scott Bahneman on Facebook and it went unanswered.
If you search news stories online, you'll find two or three articles about their being in Chapter 11 and that they're hoping to be out of it soon. Much as I loved them, I think it's extremely rude that they won't even let their customers know what's going on. No email, won't answer the phones, nothing. I bought over 500 tracks from them over a period of about three years. I'm a very loyal customer, and I'm not happy about being given the brushoff.