I've had an account with them for two years and haven't done one shop yet because I can never log in to their website. I always get a "log in failed" message when I try to log in. I'll reset my password and it'll say it was changedsuccessfully and immediately try to log in and get a failed notice. It doesn't matter what browser or computer I use , I can never get into their website. Sometimes I go months without trying to log in but I've tried off and on for two years now and nada. Anyone else have issues? I've reached out to them and occasionally they will respond but nothing they suggest works. It's so weird. I've never had this issue with out MS sites.
Try an incognito browser window or switch to another browser. I tend to have this issue in Chrome (unless using an incognito window). I've tried clearing my cache and cookies, but it doesn't seem to help unless I go back to using an incognito window there. It loads up fine all the time in Firefox at least.
I had this issue when I signed up last year as I had an account many years previously so I wondered if that was the issue. I ended up emailing Market Force and they were very receptive and their IT department had to do something but it's all good now.