Windows 7: intermittent DSL drops over the last few weeks

I'm not sure if this is a Win 7 problem, and probably isn't even an issue with the PC- at the very least, I seem to be malware-free going by running MSSE, Malwarebytes and Spybot and their inability to find anything. I also was told this is likely a line issue, not a PC issue.

my setup first- Netopia 2241N modem direct connect to the internet by DSL phone line and direct to PC via Ethernet cable. No router or hub as I only have one device online, no wireless home internet.

But the past month or so I've had intermittent DSL line disconnects- mostly at random, generally the net connection drops, the internet light goes red and it reconnects a minute later. It started at night, between midnight and 6 AM, so I wrote it off as an ISP issue. Then it started in the afternoon and has gotten worse. It stopped for a few days but has started again. I thought maybe it was the phone line splitter in my 1-year old Belkin surge protector and bypassed that, which is when it stopped but it's started again, so it may not have been that.

The 25-foot phone line cord going from the phone line splitter t the PC may be going bad, I plan to get a new one this weekend. It is old and barely plugs in right at the modem(it doesn't click into place). But fi that doesn't help... then I have to check the in-house line splitter box, the cable that goes from it to the outside junction box, and maybe the junction box.

Is there any chance this is the modem itself? Could it be overheating or old? I've had it for 6 years now. But I ran the onboard system diagnostic and everything showed as a PASS status(excluding the USB port, which I don't have connected). I changed the ethernet cable as I had a spare but my ISP says it's almost definitely an issue anywhere between their server and the modem since it's dropping the internet connection.

I tried checking with neighbors but I seem to be the only person in this area who gets land line internet straight from my ISP. Most don't own PCs and the couple that do get internet through their cell phone providers, not my ISP. I've also not noticed any actual issues with phone calls- at least, nothing that stands out. For all I know it's dropping for 1-2 seconds, long enough to affect the DSL connection but not enough to stand out in a phone call.

If this is an ISP issue, clearly they need to find it and fix it, but I also need to diagnose in-house problems. If replacing the phone cable doesn't work, and checking the junction box, splitter box and cable between them doesn't help, then they have to replace the modem- and if that doesn't help then it's their end. But with positive diagnostic results the modem doesn't seem too likely to me. The odd hours it disconnects also make me wonder if it's their end, because sometimes it'll happen repeatedly(happened 3 times in 10 minutes yesterday) but then it will go for hours without dropping.

Oh... and my upload speeds this past week have fluctuated like mad. Typically I average 60-80 kilobytes a second upload, it's been as low as 15 a second lately. But my download speeds aren't at all changed, I'm still reaching the 400 kilobytes/second average I'm used to. Speedtest.net the other day was at 0.16 upload, today it was about 0.26. But I've also noticed it up to the top average a few times too.

I accessed the modem's on-board menu. Ran diagnostic, found no errors. According to system logs the modem itself is fine and the line is okay. SNR and all that are in normal Db levels.

ADSL Line State: Up
ADSL Startup Attempts: 1
ADSL Modulation: ADSL2
ADSL Data Path: Interleave
Datapump Version: DSP 5.2.2.0, HAL 5.2.2.0
Downstream Upstream
---------- ----------
SNR Margin: 13.50 10.20 dB
Line Attenuation: 26.00 14.50 dB
Output Power: 15.83 8.58 dB
Errored Seconds: 0 0
Loss of Signal: 0 0
Loss of Frame: 0 0
CRC Errors: 0 0
Data Rate: 4509 699