You really need to narrow the problem down more. Here is a nearly complete list of possibilities of what can fail on a typical broadband connection that is experiencing intermittency:
Your margins (signal to noise ratio) have gone down and you need your lines reconditioned (some ILECs will do this, but if your ISP is a CLEC, you might not have much luck). If you can't get it reconditioned, you may need to go with a slower service. This can also be caused by bad connections on the circuit (such as the punch down at the NID/DMARC/MPOE or any jacks you have in the building). The primary symptom for this is intermittent drops in the modem (you'll see the DSL light go out on the modem). Some of these issues you can check yourself by testing the internal wiring of your building for resistance, but other things will have to be tested by your ISP.
There is voltage on the lines (DC or AC are both possible) and this is interrupting your signal. Again, only your ISP will be able to confirm this, they will do so by use of a loop test.
There is unbalance on the line. This is caused by either the Tip or Ring on the circuit being longer than the other, this wreaks havoc and causes an intermittent connection. Again, only your ISP can confirm this and it is also usually reported on a loop test.
Your modem is going bad. This is somewhat common on modems 3+ years old. Usually this is a result of the modem being in too hot an environment for too long, being plugged into an unregulated power supply for too long (either a bad power strip or wall socket), or suffering damage from a surge. Modems will just wear out at times too. If you have a test modem, you can replace it and see if the problem goes away, if it does, you know it was the modem. Sometimes, even the LAN or WAN port on a DSL or cable modem will go bad, it is rare, but it does happen.
Your LAN cable is bad. Believe it or not, LAN cables go bad frequently. Just because it worked yesterday doesn't mean it works today. A cheap tester won't be able to tell you if the cable is ok or not, the cheap ones only test pinout and continuity, what you are looking for is resistance. When copper starts to degrade, resistance on the cable goes up and can cause connection issues. You can rule out the cable simply by replacing it and seeing if the problem persists.
Your router is bad. Routers go bad frequently. And believe me, it is always more likely to be your router that has failed than the ISPs networking equipment. Routers can go bad in a multitude of ways. Most routers are really several devices all packed into one. They have a wireless access point, a multiple port switch and a router, all built into one, some routers even have a bit more than this, some a bit less. In any case, that just means many points of failure. Any port can go bad at any time, the connection between the switch and the router internally can go bad, the wireless can fail, the connection between the access point and the router internally can fail, etc. You can usually rule out a router error by directly connecting a computer to your modem and seeing if the problem persists or not, if it does, then it is not your router.
Your computer's NIC (network interface card, or LAN port) can fail. This can be tested by using a different NIC if you have one available.
Your ISP may be having issues with their DSLAM or CMTS, the device that provides layer 2 connectivity for your connection. This is usually caused by a faulty card, port or backplane on the system. This is something that only your ISP will be able to determine.
Your circuit config has been corrupted. This is something that is more common than you realize. This can be fixed typically by reprovisioning the circuit, but also sometimes requires a rebuild at the ATM. This will vary by ISP and can only be diagnosed by the ISP.
Your ISP may be having issues with their core routers or ATMs that provide Layer 3 services. This can be caused by card, port or cabling issues on these devices. When these devices fail, you will see latency, packet loss, or just a lack of layer 3 connectivity altogether. Again, only your ISP can determine this is the cause.
Your circuit may be over-utilized. Very commonly, people over-utilize their circuit. This causes latency and packet loss and can appear as a slow or intermittent circuit. Your ISP will be able to determine this, but you can also monitor your own bandwidth consumption with applications like wireshark or spiceworks.
As you can see, there are many points of failures, so just saying "loses connection" doesn't really help until you start ruling out variables. When ruling things out, always start with Layer 1. When you've exhausted all possibilities you can without the aid of your ISP, give them a call and they'll check on the rest.